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SMITHSONIAN

SCIENTIFIC SERIES ,

Editor-in-chief
CHARLES GREELEY ABBOT, D.Sc.
Secretary of the

Smithsonian Institution

Published by

SMITHSONIAN INSTITUTION SERIES, Inc.
NEW YORK

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A composite scene of living red and brown algae from widely separated
areas in the Atlantic and Pacific oceans. The brown alga is the giant
kelp (Macrocystis), a valuable fertilizer. By E. Cheverlange

OLD AND
NEW PLANT LORE

A SYMPOSIUM

By
AGNES CHASE
A. S. Hitcucock
Earu S. JoHNSTON
J. H. Kempton
Etisworty P. Kivuip
DanieEL T. MacDoucat
ALBERT Mann
Witiiam R. Maxon

VOLUME ELEVEN
OF THE

SMITHSONIAN SCIENTIFIC SERIES
1931

[Printed in the United States of America]
All rights reserved

Copyright Under the Articles of the Copyright Convention
of the Pan-American Republics and the
United States, August II, 1910

CONTENTS

PAR
THE WORLD OF PLANTS

By
A. S. Hireucock

I. FuNDAMENTAL Lire PROCESSES IN PLANTS .
Il. How Puiants SEEK THE LIGHT
Ill. How Pianrs REPRODUCE a a ae
IV. Pranr Movements AND CARNIVOROUS
PLANTS
V. Prant Societies
VI. How PLANTS ARE Raven
VII. How Priants are Usep sy Man
BIBLIOGRAPHY

APPENDIX: GROUPING OF SOME BETTER-
KNOWN PLANTS BY FAMILIES

Paro it

SYSTEMATIC BOTANY: ITS DEVELOPMENT AND

CONTACTS

By
WitiiaAm R. Maxon

I. THe OrtciIn AND DEVELOPMENT OF SYSTEM-
Atic BoTANY .
Il. Tue Contracts AND Sonne OF re
BoTany
BIBLIOGRAPHY

133

148
164

UT,

ILL.

Til,

Parr [ii
PLANTS OF THE SEA

By
ALBERT MANN

GENERAL CHARACTERISTICS
KINDS OF ALGAE

Uses or THE ALGAE
BIBLIOGRAPHY

Part IV
GRASS

By
A. S. Hireucock and AGNES CHASE

GRASSES THE Basis oF CIVILIZATION
GRASSES THE Basis or WEALTH
Tue PLAce OF GRASSES IN THE PLANT Worn
BIBLIOGRAPHY

Parr V
DESERTS AND THEIR PLANTS

By
DaniEL TrREMBLY MacDouca.L

CHARACTERISTIC FEATURES OF DESERTS

ORIGIN AND DEVELOPMENT OF DESERT
PLANTS :

ADAPTATION OF Pee AND Anes TO
DEsERT CONDITIONS .

BIBLIOGRAPHY

167
175
184
197

Pagar Vi
THE DEPENDENCE OF PLANTS ON RADIANT

ENERGY
By
Faru S. JoHNSTON
I. Licut anp PLant NutritTIon 287
IJ. Licur anp GrowTH Vans Wkor sel
Pi se HOTORROPISME Wa). se pane eat ks LP OF
BIBLIOGRAPHY Rug

Part VII

MAIZE, THE PLANT-BREEDING ACHIEVEMENT
OF THE AMERICAN INDIAN

By
J. H. Kempton

I. THe DomESTICATION OF PLANTS AS A MEAS-

URE Om C1 MLIZAMION (ei 204 cy, 02) Smo naa
He Trey Oricrn or MAIZE Wiis ail Anh amg
EB TIOG RARELY pec Mey lr ried isp ling! ral in eS AO
Part VIII
BOTANICAL EXPLORATION IN SOUTH AMERICA
By
E.uisworty P, KItip
I. A New Fre.p ror AMERICAN BoTaNISTS . 353
De VOR K IN HE SHTERD ICO li BOG ve) gel 2369
BIBLIOGRAPHY area, (UP CtICR Say? Malle aaa

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19.
20.
21.
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24.
Des

Lo ee ee I ee ee ee oe |
SIDA OP AOS SIDA pm

PEewUst RALEONS

LIST OF PLATES

Composite scene of living red and brown algae . . Frontispiece

Part I

Baobab tree, showing disproportionate growth of trunk
Phenomena incident to air requirements of tree roots
Dry cypress swamp, Texas . ;

Base of a mora tree in rain forest of Bech Cane
Clump of paper or canoe birches

Magnified cross section of trunk of pine beeeh
Wisteria climbing on porch of house in Washington.
Banyan tree with air roots sent down from branches
Floral parts of a lily be

Flowers of night- blooming cereus .

Yucca growing on Mount Wilson, Galramias
Venus’s-flytrap i

Live oak with Spanish m moss hanging ene Reaches:
Silver-sword growing in lava in volcanic crater .

Wheat showing stems and leaves infected with black ont 4

Kernels from healthy and from rust-infected wheat
Under side of a fern leaf, showing spores .
Part of magnified cross section of a palm stem

Part II

Theophrastus, ‘‘Father of Botany”

Linnaeus at the age of 67 ha

Live-forever, originally from Mexico . . ;
Main hall of herbarium, British Museum, London .
Mounted plant specimen from National Herbarium.
Pure stand of Douglas fir

Grove of Deglet Noor date palms 1 near - Indio, California

Part III

Brown algae Lessoniopsis and Postelsia, from Alaska
Brown alga Sargassum cymosum, from Florida
Brown alga Pelagophycus porra, from Pacific Coast .
Brown alga Agarum Turneri, from Massachusetts
Red alga ‘Polysiphonia violacea, from Marthas seattnts
Coralline algae growing on sea ‘shells ;

Three coral-like red algae from subtropical waters .
Living diatoms from widely separated waters.
Composite scene of living red and green algae

Red alga Gigartina microphylla, from California .
Lamina of brown alga Alaria fistulosa, from Alaska.
Red alga Polysiphonia Baileyi, from California .
Red alga Laurencia paniculata, from Florida.

Fossil and living diatoms

Part IV

Field of sugar cane, Hawaiian Islands.

Herd of pack llamas in the Andes, Peru .

Chinese Indian rice outside the walls of Nanking
Dwarf Indian rice converting marsh into meadow
Spartina Townsendii in the Netherlands .

Clump of bamboo in China.

Uses of grasses in China.

Sheep herders’ huts in the high Andes, Peru .
Pampas grass, Hawaiian Islands

Sheep feeding on the high plains of the Andes, Peru.

Part V

Caravan traveling in Libyan Desert, Africa .
Salton Sink, California, 240 feet below sea level .
Wind ripples in sandy soil of Mohave Desert, California

Rounded wind-worn hillocks in the eed eere Africa

Typical desert vegetation, Arizona

Typical desert vegetation, Mexico.

Vegetation in the Mohave Desert, California.
Succulent Coralluma near Port Sudan, Red Sea .
Principal types of desert vegetation

Watering animals at pits dug in stream bed, Upper Egypt.
Vegetation at foot of Santa Catalina Mountains, Arizona .

Typical vegetaticn in the Mohave Desert, California
Altar-candle trees, Sonora, Mexico .

Part VI

Absorption spectra of the two chlorophylls

Healthy tomatoes on plants grown in water cultures

Undernourished and normal leaves of tomato

Tomato plants, showing effect of boron in solution .

Influence of light on opening and closing of stomata

Mammoth tobacco, a short-day plant from southern
Maryland Fe Prete fash ae emia ne earn Re Tet nee

Effect of duration of light on Mammoth tobacco plants

Reaction to light of parts of a mustard seedling .

Plant photometer box for study of phototropic bending.

Oat seedling, showing reaction to blue and to red light

Parr VII

Color patterns in corn ears grown by Indians of Southwest.
Prehistoric ears of corn from Utah and from Peru
Peruvian ears of corn, fossil, prehistoric, and modern
Seeds of corn showing five color patterns .

Ear of Cuzco corn, peculiar to Peru er he
Color patterns in corn ears grown by American Indians
Two relatives of maize, Tripsacum and Euchlaena .

A normal corn plant. SS xt ietre, dient a) ae te
Tassels of Euchlaena and of Euchlaena-maize hybrids
Evidence for fusion as origin of corn ear .
Longitudinal section through ear of ramose corn.
Tassels of Euchlaena and of Euchlaena-maize hybrids
Examples of a color mutation in corn . mera ye
Aztec urn bearing facsimiles of excellent ears of corn

Part VIII

Vegetation of the subtropical zone in Colombia .

Wax palms of the Quindio trail, Colombia

Lupine from the Paramo del Quindio, Colombia.
Frailejones (little friars) on the Paramo del Quindfo.
Distichia tolimensis on the Paramo del Quindio .

Indians bringing plant specimens, Yurimaguas, Peru
Preparing planejspeeimensy wy <1) 6 hs) ch
Expedition crossing the Péramo de Santurban, Colombia .
Caravan of mules arriving at Popaydn, Colombia
Transporting supplies across a river in Colombia
Transplanted orchids growing on wall of house .

288
294
295
298
299

304
395
308
312
313

369
370
371

19.

Ln ee ee oe oe
SI ARE OPH OD SI ANA P

LIST OF TEXT FIGURES

Parr I

Diagram of principal organs of a seed plant .
How areas of growth are determined .
Section through tip of a growing root .
Manometer to measure root pressure .
The extensive root system of a wheat plant .

Cross and longitudinal sections through a ae stem .

Growth of a woody stem for ten years.

Four-ranked arrangement of leaves and a leaf mosaic .

Twigs of trees, showing leaf scars and buds .
Branch drawing up water to supply loss from leaves
Section through a leaf and epidermal cells of a leaf .
Dodder parasitic on a hop vine

Leaf mosaic

Climbing mechanisms of plants. :

A mold, showing the branching of the filaments .
Pollination of the tape grass aoe
Pollination of the sage by a bumblebee
Pollination of the lady’s-slipper.

Pollination of the yucca. -

Contrivances for throwing seed

Dispersal of seeds by wind .

Fruit of the burdock.

Embryo and seedling of corn or maize. :
Seeds and seedlings of the bean, pea, and oak
Germination of the red maple . ;
Rootstocks or rhizomes...

Runner or stolon of the strawberry

Tubers of the potato.

Bulb of a lily . ;

Grafting and budding

Sensitive plant

Sargassum. .

Lichen of the leafy sort .

A moss, showing capsules that contain the spores
A fern, showing coiled young fronds

Part IV

Leaves of grass and red clover, showing areas of growth

Heads of grasses .
Sugar cane

Stalk of maize or Indian corn .

Tuft of grama grass .

Kentucky blue grass . ;
Bermuda grass, showing habit of growth ;
Heads of timothy and orchard grass
Beach grass, an excellent sand binder .
Villainous native grasses.

Villainous introduced grasses

Broadleaf Uniola.

Branch of a common flowering plant and spikelets of grass.
Buffalo grass spreading by stolons .

Part V

Map of the world, showing principal arid areas .

Parr VI

Effect of light on position of chlorophyll bodies.
Diagram showing phototropic bending of coleoptiles

Part VII

Inflorescence and section of a leaf of Tripsacum aa
Inflorescences of Tripsacum and Euchlaena ‘
Central spike of a maize tassel and tassel of Euchlaena.
Corn-plant design on a clay vessel in Peru

254

291
309

332
334
338
347

:
ry

Pacer aL
ee ey ty. (Meigen

LR 2. aly
if i US Y

Part I
THE WORLD OF PLANTS

A. S. Hircucock

Principal Botanist in charge of Systematic Axzrostology
United States Department of Agriculture
Custodian, Section of Grasses
United States National Museum

vai
{é

Degye

Yay on

CHARTER

FUNDAMENTAL LIFE PROCESSES IN
PLANTS

Tue study of plants is called botany. The word botany
may suggest a vague world outside of man’s ordinary ex-
perience, a world dominated by long and fearsome Latin
names. As a matter of fact, forbidding Latin names form
a very small part of botany and need repel no one. Fur-
thermore, the average man actually has more knowledge
of botany than he realizes. Agriculture, horticulture,
gardening—even the making of a lawn—are applied
botany. He knows also that potatoes, rice, and bread
contain starch and that sweet fruits and sweet potatoes
contain sugar; and he realizes, if he gives the matter suffi-
cient thought, that starch and sugar are plant products
and that plants are a great factory in which much of our
sustenance is manufactured. This world of plants, with
which we animals share the earth, is of such interest and
beauty as to be well worth at least enough study to open
our eyes to its everyday marvels. So much study we
propose to give here.

We shall consider plants from three standpoints: first,
how plants live and grow and reproduce themselves, how
they scatter their seed, how they are adapted to their en-
vironment, how they are distributed over the face of the
earth today, and how they were distributed in ages past.
All this is, in a broad way, plant physiology. Next, we

lia]

THE WORLD OF PLANTS

shall consider how plants are related to each other through
a common ancestry reaching back millions of years. The
classification of plants is an attempt to show this relation-
ship, and is called systematic botany. Finally, we shall
consider the relation of plants to man, showing how man
derives his food, clothing, and shelter, his necessities and
his pleasures alike from the plant kingdom. The study of
the uses of plants is called economic botany.
Plants, like animals, can not exist without air, food, and
water; but, though
erninel $4 thew. requirements
and life processes
are similar to those
of animals, their
organs are not
analogous. Plants
breathe, but they
have no lungs; they
digest food, but have
no stomach; the
Qy | | pZ- @4""* crude sap ascends
their stems and the
Vascular system elaborated sap is
diffused downward
from the leaves, but
they have no heart
to pump it nor any
real circulatory sys-

tem; they respond

Fic.1. Diagrammatic representationof to) gtimuli—for ex-

the principal organs of an ordinary seed
plant. After Holman and Robbins

ee Root bas

eesiel sees KOOLLCID

ample, a tendril curls
when it touches a
support, and a leaf turns toward the light—but they have
no brain nor nervous system. Nevertheless plants do have
organs that are specialized for certain purposes, and it ts
interesting to note how the structure of an organ is
adapted to its function.

[ial

PLATE 1

growth of the trunk, on the

The smaller objects in the branches are fruits,
gs. Photograph by Hitchcock

f hollow lo

A baobab tree, showing disproportionate
the larger are beehives made o

dry plains of Africa.

FUNDAMENTAL LIFE PROCESSES

To illustrate the life processes of higher plants, let us
take acommon tree. The three primary sets of organs are:
the roots, the trunk and its branches (stems), and the
leaves (Fig. 1).1 The roots hold the tree in place and absorb
water and nourishment from the soil. The trunk supplies
a channel for the flow upward and downward of the sap
and mechanically is so built as to support an adequate
leafage, and yet not be top heavy; it divides into branches
and branchlets, successively smaller, finally ending in the
twigs. The branches are large at the base and taper toward
the extremities, thus giving a strength and suppleness that
enable them to withstand storms. This is made easier for
them by the fact that the twigs and leaves yield to violent
winds, bending before them and presenting a minimum
surface to the blast. The leaves are borne only on the
twigs, that is, on the branchlets of the current year’s
growth; (however, the leaves may persist for more than
one year). In a manner to be described later, the leaves
elaborate food for the plant, using water from the soil and
carbon dioxide from the air, the elaboration taking place
only in the sunlight. The leaves are flat, so that they pre-
sent the greatest possible surface in proportion to their
mass to light and to air, and they are so arranged on the
twigs that they catch the greatest possible amount of sun-
light. If the tree stands by itself so that light comes to it
from all sides, the branchlets are evenly distributed in all
directions and, if left untrimmed, they may reach nearly
to the ground. In such a tree scarcely a ray of sunlight
penetrates to the center of the mass of foliage and it casts
an almost unbroken shadow upon the ground, showing
that the leaves catch every ray of sunlight. The leaves at
the periphery are full of vigor; those toward the inside get
along as best they can with diffused light; if the shade 1s
too dense they give up and fall to the ground. If the tree
is part of a forest the struggle for light becomes severe and

1 Cordial acknowledgment is made to the United States Department of Agriculture
for the loan of Figures 1, 3, 4, 38, 39, 49, 42, 47, and 49.

[3]

THE WORLD OF PLANTS

leaves are found only on the crown at the top. If the tree
grows on the bank of a stream it may be forced to send
slender branches far out over the water to seek light from
the side.

Roots

The roots have two functions: first, to hold the tree in
place and support it against bending and twisting by
storms; second, to absorb nourishment from the soil.

Fic. 2. How areas of growth are determined. Left, young root

marked with equidistant lines, and their displacement by subse-

quent growth; right, young leaf marked off in squares, and their
displacement by subsequent growth. After Kerner

Roots branch extensively but only the ultimate branchlets
grow in length, the growing area being just back of the
tip (Fig. 2). It is obvious that if roots grew in length in
other areas the side branches would be scraped off by the
resistance of the soil. The part of the fine rootlets where
growth takes place may be only an inch, or even less, in
length. To protect the end of the tender young root as
it pushes through the soil there is a little cap which is
being constantly repaired by new cells in front as the worn
cells are sloughed off the sides (Fig. 3). A short distance
back of the growing end there is an area on which root

[4]

FUNDAMENTAL LIFE PROCESSES

hairs are produced. To the naked eye these root hairs
look like white fuzz or velvet, but when slightly magni-
fied the fuzz is seen to consist of slender hairlike cells.
The area of root hairs moves
forward with the growth of the
rootlet, the old hairs dying off —U

behind and new ones forming in ail ia Be
front. These minute organs have eB ae

the power to absorb soil water,
that is, rain water that has
filtered through the earth and
dissolved small quantities of
whatever minerals are contained

attOges
re

om 3 Ty
. . . (4 : cam fof
in the soil. The combined ab- \aaes ed eee
sorbing action of millions of root ae Bente enemy

hairs sets up a_ considerable : i]
pressure, which tends to force
the soil water, or sap, up through
the trunk and into the branches.
Root pressure, as this force is
called, can be measured by
cutting off a small tree a short
distance above the ground and
attaching a measuring apparatus
(manometer) (Fig. 4). The pres- Fic. 3. Section through
sure may at times be as much as___ tip Of @ growing root.
fifty feet. (equal) to’ that! of ia ee oan ees ene
: e rootcap, at
column ofiwatenfiity fect: high)s-\sh.. hase of lrhiehis the
In young plants of corn or wheat growing point. After
root pressure causes drops of — Holman and Robbins
water to exude from the unex-
panded tips of the young leaves during the night.
Early in the morning the drops sparkle on the points
of the leaves and are usually taken for dew drops.
rel disappear by evaporation under the influence of
the sun.

Roots may grow to a considerable distance in search of

THE WORLD OF PLANTS

water; those of the alfalfa plant, for example, have been
found occasionally to extend to depths of more than fifty
feet, though the plant itself may be only two or three feet
high. The roots of willows become troublesome at times

Manometer

Fie. 4:
to measure root pres-
sure. As the roots
force water into the
glass tube the mer-

cury rises. After
Holman and Robbins

by growing into tile drains and
there branching profusely until
they fill a section of the drain like
a large plug and stop the flow of
water. The guilty willow tree may
be many yards from the plugged
drain.

Although roots grow in length
only at the ends, every part of them
may grow in thickness. In most of
our forest trees this “secondary”
growth is very evident. The effect
of the thickening of roots under
pavements, where the bricks,
stones, or even cement slabs are
raised, is a familiar sight. Roots
penetrating crevices of rocks and
afterwards thickening may scale
off slabs or layers of the rocks, thus
aiding in converting them into
soil.

The tree obtains its food from the
soil and the air. The dissolved min-
erals in the soil water constitute the
earthy part of this food, and this is
the part that is left as ashes when the
wood is burned. But while the food

offered in any given spot is the same for all the plants
growing there, the roots to a certain extent make a
selection, different species absorbing widely differing
quantities of minerals. An individual of one species may
take in twice as much calcium, for example, as its nearest
neighbor. When the sap within a plant is saturated with

[6]

FUNDAMENTAL LIFE PROCESSES

a given mineral its roots absorb
no more of that until the
plant in its vital processes
uses up what it has. Thus a
plant may have use for calcium
sulphate, possibly because of
the sulphur contained in the
mineral. The calcium of the
calcium sulphate (which is
soluble) may be separated
from the sap in the form of
the insoluble calcium oxalate
and stored as crystals, thus
reducing the amount of cal-
cium sulphate in the sap,
whereupon the roots absorb
more of this substance to make
up the deficiency. As a result
the plant takes up much more
calcium sulphate than its neigh-
bor of some other species. It is
because crop plants may take
different amounts of constit-
uents from the soil that they
may require different fertil-
izers to supply their need.
Certain elements are essen-
tial to the proper nourishment
of plants. This has been
demonstrated by growing
plants in jars of water to
which have been added defi-
nite amounts of mineral con-
stituents. In these experiments
it was shown that the want
of certain elements would
cause aberrations in growth

lial

li
itis

Fic. 5. The extensive root
system of a wheat plant.
After Weaver

THE WORLD OF PLANTS

or function. For example, when iron was_ lacking
the plant could not produce the green coloring matter
(chlorophyll). It was also shown that higher plants need
magnesium, calcium, potassium, phosphorus, sulphur, and
nitrogen as well as iron. Furthermore, certain plants
require minute quantities of other elements, such as
boron, manganese, copper, and zinc. Usually virgin soils
contain sufficient quantities of all these minerals in the
form of “salts,” carbonates, sulphates, phosphates, sili-
cates, and so on, or as oxides or hydrates. The important
element, nitrogen, comes into the plant usually in the
form of soluble nitrates, a fact which has an important
bearing on the deficiency of this mineral in crop-bearing
soils. Plants growing under natural conditions, through
the shedding of their leaves and by their disintegration
when they die, return their mineral content to the soil.
Crop plants do not do this, as a large part of each plant
is removed in harvesting, and the mineral content is lost
to the soil. Continued cropping may soon cause a de-
ficiency of certain elements, one of the first to give out
being nitrogen, because most of that element present in
the soil is in the form of soluble nitrates. All soils con-
tain an inexhaustible supply of sodium, magnesium, and
silicon, but deficiencies in nitrogen, phosphorus, and
potassium may be readily brought about. The agricul-
turist must supply the deficient elements by applying
fertilizer.

There is usually enough iron in all soils to supply the
needs of plants, but a remarkable case of iron starvation
was brought to light a few years ago in connection with the
culture of pineapples in the Hawaiian Islands. On certain
soils the pineapple plants failed to produce sufficient
chlorophyll and were therefore pale or bleached, a condi-
tion known as chlorosis. Investigation showed that,
though there was plenty of iron in the soil, the large
amount of manganese present prevented the plants from
absorbing the iron. This condition was remedied by

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FUNDAMENTAL LIFE PROCESSES

spraying the plants with an iron solution. The iron was
absorbed by the leaves, and the plant was able to manu-
facture the normal amount of chlorophyll.

In order to function properly roots must have air.
Under ordinary conditions soil is loose enough to contain
sufficient air in the interstices, but any abnormality that
affects the air supply threatens the life of the plant. Thus
trees not accustomed to an excess of water will be killed
if the ground is submerged for a considerable length of
time. They may withstand flood-waters, which eventually
recede, but if the water stands permanently above the
roots, thus excluding the air, they will be killed. The
effect of permanent submersion was well illustrated in
Panama, where all the forest trees flooded by the waters
of Gatun Lake (Plate 2, left), impounded by the great
Gatun Dam, were killed. A familiar example of the
effect upon trees of a reduced supply of air to their roots
is presented by the shade trees of city streets. A piece of
open ground is left around the tree when the sidewalks are
laid. This open surface may supply sufficient air to
small trees, but as the trees grow larger they require more
air. In residential sections roots will usually penetrate
beneath the sidewalks to the open front yards near by
and thus obtain air as well as nourishment. But in the
business sections of the city there may be no open spaces
into which the roots can penetrate. The result is retarded
growth and ultimately the death of the trees. Smoke and
noxious gases and the lack of proper nourishment may also
help to bring about these results.

At one place on the north side of Park Road in the city
of Washington there is a high terrace. At the inner edge
of the sidewalk is a wall six feet high, above which the
ground slopes up steeply. On the other side of the street
the houses, each with a small grassy yard in front, are
nearly on a level with the sidewalk. Many years ago a row
of elm trees was planted along each side of the street.
The trees on the lower side grew normally because the

[9]

THE WORLD OF PLANTS

roots could utilize the front yards of the houses. Those
on the terrace side of the street, though of the same age as
the others, were much smaller. They appeared to be only
a third as old as the others and were in poor condition.
These trees sent their roots under the sidewalk and under
the wall but were unable to find the air they needed
because they were still many feet below the surface.
Within recent years, however, the stunted trees have
taken on new life and are growing vigorously. Evidently
the roots have at last reached up to the surface soil.

Trees growing on a lot which is to be filled in can be
preserved by building a well around each tree to prevent
the roots from being entirely cut off from their air supply.
If the filling is not too deep the roots may ultimately reach
an air supply at the surface of the added soil.

Trees that grow in swamps and so have their roots sub-
merged may have special means for conducting air to the
roots. The knees of bald cypress (Taxodium distichum)
(Plate 3) are branches of the roots that reach above the
surface of the water and conduct air below. At low water
a cypress swamp with the numerous knees sticking up
to a height equal to the usual level of the water in the
swamp presents a curious aspect. The common mangrove
(Rhizophora mangle) conducts air down through its tangle
of stilt roots. Other mangroves (for example, 4vicennia
nitida, Plate 2, right), produce a swarm of wertical roots
for carrying air. These are exposed at low tide and sub-
merged at high tide. Swamp and marsh plants in general
have some contrivance for conducting air to the roots.
Usually there are air channels or spongy tissue within
the stem, leading down to the root system; a few plants,
such as winged loosestrife (Ludvigia alata), produce
spongy or corky tissue on the outside of the stem from a
short distance above the water line to a considerable
distance below it.

Man is constantly attempting to change soil conditions
for the benefit of his crop plants. He mulches the surface

[10]

FUNDAMENTAL LIFE PROCESSES

of the soil with hay or straw, or loosens the top soil, giving
it a “dust mulch,” to prevent too much evaporation. He
supplies rales in order that his crops may have proper
and sufficient food. In regions where the rainfall is in-
sufficient he supplies water by irrigation. Sometimes in
his efforts to improve on nature he makes serious mistakes
through ignorance of the principles involved. A striking
example of this is seen in the effect of over-irrigation in
some of our western States. Thinking that if some water
is good for crops, more would be better, some ranchmen
were in the habit of flooding their fields with irrigation
water, giving the crop much more water than it actually
needed. The excess evaporated, but, of course, left
behind its mineral content. Shas irrigations and
evaporations brought more and more mineral—or “alkali,”
as it is called by the ranchmen—to the surface, until this
became so concentrated that crops suffered. The more
the irrigation the worse the result. Finally crops were
inhibited by the excess of mineral and the fields became
“alkali” wastes supporting only certain resistant native
plants of no value to the ranchman. Investigation
showed that the effects of over-irrigation could be gradu-
ally remedied by drainage. The reverse process now
took place; the excess of irrigation water dissolved the
“alkaly” and carried it away through the drains.

STEMS

The stem or trunk supports the leafy crown of the tree
and supplies it, through branches and twigs, with the
minerals and water absorbed by the roots. The stem
consists of an elaborate structure of strong hard wood, a
system of specialized tubes, and a protective covering of
bark. But, however tall and stately the tree may be, 1 the
trunk is made up, as is the smallest herb, of minute cells.

A typical vegetable cell has a wall of frm material
(cellulose), and the cavity is filled, or partly filled, with
protoplasm, which is the living substance of the plant.

ear |

THE WORLD OF PLANTS

Protoplasm itself, as seen under a high-power microscope,
is a colorless fluid, denser than water and resembling the
white of an egg. In active plant cells it can be seen, be-
cause of the small granules it contains, to move around
the cell in streams. Within the cell are various bodies: the
nucleus, a dense portion in which the directive power of
the cell probably lies; the chlorophyll granules that give
the green color to plants; other color bodies; and, some-
times, oil drops, crystals, and other substances. When
first formed, cells are much alike but they soon develop
into the shape and structure necessary to perform the par-
ticular function for which they are destined.

If we examine with a microscope a cross section of a
mature twig of any common tree, we can see that it is
marked off into five circular zones, one inside the other.
At the center is the pith; second comes a zone of wood;
third, a thin layer of growing cells, called the cambium;
fourth, a zone of young bark; and finally, the epidermis
(Fig. 6). The cylinder of pith at the center consists of
soft, roundish, thin-walled cells, the contents of which
soon die and are replaced by air. The zone of wood just
outside the pith is made up of two kinds of cells. One
kind is thick walled, several times longer than wide, and
has pointed, overlapping ends, which enable each cell to
cohere firmly with its neighbors and so to give strength
to the stem. The cells of the second kind are larger than
wood cells and coalesce to form long tubes, which run
lengthwise through the wood. The tubes are usually
strengthened by spiral ridges on the interior of the walls,
for which reason they are often called spiral ducts. Jump-
ing for a moment the thin circle of growing cells, we find
a zone of young bark and outside of this the epidermis.
The young bark, like the wood zone, is made up largely
of two kinds of cells; bast cells, which are thick-walled
like the wood cells but proportionately much longer (also,
though thick walled, they are flexible); and thin-walled
cells forming tubes. These tubes have sieve-like openings

[12]

FUNDAMENTAL LIFE PROCESSES

in the walls or partitions, through which nutritive ma-
terial is carried.

Between the wood and the bark is the all-important
cambium, a thin layer of growing cells, quite regular in

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Fic. 6. Cross and longitudinal sections through a woody stem.
After Kerner

shape and only a few cells thick. It is continuous from
the twigs through the trunk and large roots to the small
branches of the roots. To the cambium the stem owes
its growth in thickness. It is an undifferentiated growing
layer. When active the inner layer of cells is changing

[13]

THE WORLD OF PLANTS

into wood, the outer layer into bark, while the central
part continues to be cambium. The growth in diameter
of the twig, branch, or trunk means that the cambium is
adding wood to the outer circumference of the wood zone,
and bark to the inner circumference of the layer of bark.
As the youngest and largest layer of bark is the inner-
most, the outer bark is always too tight and is continually
being cracked and split by the pressure from within. The
trunks of many of our common trees, such as the oak,
maple, and walnut, become furrowed. The bark of the
planetree or sycamore (P/atanus), scales off in large plates;
that of the canoe, or paper, birch (Betula) peels off in
beautiful sheets (Plate 5). In regions where there is a
distinct winter season, during which the tree is dormant,
the cambium grows most rapidly in the spring, when the
young twigs are forming. The farm boy knows that this
is the time to make willow whistles, and he cuts a young
twig and hammers it with the back of a pocket knife. This
crushes the juicy cambium, the bark readily slips off, and
the makings of a whistle are at hand.

The greater part of the trunk of a large tree is no longer
living matter; a layer of sapwood just inside the cambium,
the cambium itself, and a layer of bark just outside are all
of the trunk that is really alive. The inner wood and
outer bark are dead and serve the tree only mechanically.
The sap, that is the soil water absorbed by the root hairs,
ascends through the young wood.

Trees are killed by girdling, which consists in removing
a band of bark a few inches wide, and deep enough to in-
clude the cambium, from all the way around the trunk.
This interrupts the downward movement of the elaborated
sap by which the roots are supplied with nourishment, and
death follows as soon as the nourishment stored in the
roots has been exhausted. Girdling to this depth does not
interfere with the upward current of water from the
roots; hence the leaves do not wilt. But if the girdling is
deep enough to cut through the young wood (sapwood)

[14]

PLATE 4

Base of a mora tree in the rain forest of British Guiana. The buttresses
support the tall trunk. Photograph by Hitchcock

FUNDAMENTAL LIFE PROCESSES

the leaves wilt at once.
Trees girdled in sum-
mer usually die before
the following season.
Because of the rapid
growth in the spring
the tubes in the wood
are much larger at that
time, but decrease in
size as the season ad-
vances (Plate 6). The
abrupt transition from
thecompact fallgrowth
of the wood to the
lagge. ‘tubes)(/of «the
spring growth produces
a well-marked ring
(Fig. 7). Normally one
such ring is formed
each year, so that the
age of, a) ticemean) be
told by counting the
rings in the wood. It
is by the number of
rings that we know
our giant sequoias
(Sequoia gigantea) to
be from two thousand
to three thousand years
old. These rings even
bear witness to changes
of climate in ages past.
Dr A. .E.., Douglass,
of the University of
Arizona, has found
that the thickness of

INZY

W9B7 654321 6 2355578910

Fic. 7. Diagrammatic represen-

tation of the growth of a woody

stem for ten years. The concentric

rings show the age of the trunk at

any given height. After Holman
and Robbins

[15]

THE WORLD OF PLANTS

the rings varies according to the dryness or humidity of
the growing seasons. He has shown that characteristic
thickening or thinning of tree rings indicates that in
former centuries long periods of drought alternated with
long periods of humidity. Doctor Douglass has also
made tree rings serve as calendars of past events. Com-
paring the series of rings formed several centuries ago by
old trees recently felled with series in the wooden beams
found in the homes of the cliff dwellers and other ancient
peoples of the Southwest, he has succeeded in accurately
dating events in the lives of these aborigines that took
place a thousand years ago. Thus he has determined that
the “Cliff Palace”? was founded in the year 1073, and that
“Pueblo Bonito” flourished from gtg to 1130. Further
studies by this method may make it possible to fix with
approximate accuracy dates reaching back two or three
thousand years.

Although the trunk and its branches increase in girth
throughout the growing season, only the young twigs
increase in length, and this increase takes place during a
short period. In the climate of Washington the year’s
linear growth in the twigs of most trees 1s completed by
the first of July and the buds of the succeeding year are
already fully formed. A twig grows in length through-
out and not merely at the end as does a root. A leaf bud
is a miniature twig compressed into a small space. The
young leaves, or the beginnings of them, are already there,
crowded together on the very short axis which is to elon-
gate into the stem. The bud is snugly covered by over-
lapping scales which protect it from drying out. In the
spring the buds swell and throw off the bud scales. The
axis of the bud increases both in length and thickness
and separates the expanding leaves.

After the twig has attained maturity all linear growth
ceases. Tree trunks are sometimes used as “live’’ fence
posts to which fence wire is stapled. As the years go by
the distance between the wires remains the same, showing

[ 16]

PLATE 5

Clump of paper or canoe birches, the bark of which peels off in thin
sheets. Courtesy of the U.S. Forest Service

PLATE 6

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Cross section of trunk of a pine tree as seen under a microscope, showing
the annual rings. Courtesy of the U. S. Forest Products Laboratory

FUNDAMENTAL LIFE PROCESSES

that there is no increase in the length of the trunks,
though sometimes the whole tree is lifted several inches
out of the ground by the growth in thickness of its own
roots. The fence wire may become deeply embedded in
the bark as the trunk increases in girth.

In the maple tree it can readily be seen that the leaves
grow opposite to one another on the twigs (Fig. 8, left),

Fic. 8. Left, twig of maple, showing the four-ranked arrange-
ment of opposite leaves; right, elm leaves illustrating a leaf
mosaic. After Kerner

but in many other trees the leaves may seem at first
glance to be scattered at random. But the arrangement of
leaves is foreordained in the bud and is the same for all
plants of the same species. They may be opposite as in the
maple, buckeye, and lilac, or alternate as in the elm. In
the opposite arrangement the leaves are in pairs, one on
each side of the stem. But successive pairs stand at right
angles to each other, the leaves thus being four-ranked
upon the individual twigs.

In the alternate arrangement, in which there is but one
leaf at a node (the point whence the leaf springs), there are
two principal types, the two-ranked and the five- or eight-

Pa, |

THE WORLD OF PLANTS

ranked. In the two-ranked arrangement, the leaves are on
opposite sides of the stem, but one above the other, thus
bringing the third leaf above the first on the same side of
the stem, the fourth above the second, and so on. Ex-
amples of this are the elm, the linden or basswood (Ti/ia),
and the mulberry. It is a curious fact that the leaves so
arranged are usually unsymmetrical at the base and turn
on their stalks (petioles) so as to lie in one plane. The
larger lobe at the base lies next to the twig and over it,
thus filling up the space between its neighbors and utilizing
the light.

In the five-ranked type the leaves are arranged in a
spiral. Starting with the lowest leaf on the twig, the next
leaf above is two-fifths of the distance around, the third
one is four-fifths the distance, the fourth one, still going
around the same way, is six-fifths, the fifth, eight-fifths,
and finally the sixth is ten-fifths, or twice around the twig
and stands directly above the first (Fig. g, left). The
leaves are, therefore, in five rows as one looks down the
twig from above. The eight-ranked type differs from the
five-ranked in that the spiral goes three times around the
twig, bringing the ninth leaf above the first. The five-
ranked and eight-ranked arrangements may sometimes be
found on the same tree. Nearly all trees with alternate
arrangement of leaves that are not two-ranked are either
five-ranked or eight-ranked, or both, though in some trees,
such as the pine, the arrangement is more complex. The
twigs of any tree are arranged in the same order as are
the leaves, for buds are borne normally only at the ends of
twigs and in the axils of the leaves. (The axil is the
upper angle between a leaf and the stem bearing it.)
With this in mind we are able to determine whether an
organ is developed through the modification of a leaf or of
astem. Thorns, for example, may be derived from leaves
or from stems (sometimes from other parts). If they are
derived from leaves (as in the barberry), they will have
buds or branches in their axils; if they are developed from

[18]

FUNDAMENTAL LIFE PROCESSES

stems (as in the honey-locust), they will spring from the
axils of leaves. The prickles of the blackberry, raspberry,
and rose are irregularly distributed over the stems and

Fru/t Scar

Leaf Scar. A? th 7 %
Bundle Scar. We \

ee ° be 2.

‘
p / years growth

Fic. 9. Left, twig of walnut, showing five-ranked leaf scars, each

with a bud in its axil, and diaphragmed pith; right, twig of horse

chestnut, showing buds, leaf scars, and other parts used for dis-
tinguishing trees in winter. After Blakeslee

can be peeled off with the bark showing them to be out-

growths of the epidermis and cells immediately beneath.
The nature lover who enjoys the beauty of trees in

winter will find much of interest in the study of winter

[19]

THE WORLD OF PLANTS

leaf buds. Buds, bud scales, and leaf scars are almost as
characteristic of a tree species as are its leaves; in fact, the
scales are but modified leaves. In northern climates
nearly all buds are covered by water-tight scales, which
protect the tender twiglet from injury by moisture and
from evaporation in the cold dry winds of winter. The
sight of magnolia buds wrapped in gray fur overcoats, or
the buds of slippery elm wrapped in little brown blankets
might lead one to suppose that these coverings are pro-
tection from the cold, so prone are we to personify every-
thing, even plants. But plants are not “warm-blooded,”
so blankets can not keep them warm; they must take the
temperature of the surrounding air.

As bud scales enlarge in the spring their derivation from
leaves becomes evident. The shellbark hickory and its
relatives have large buds with numerous bud scales which
show the transition from bud scales to ordinary leaves.
In the hickory and horsechestnut the expanding bud
scales take on lovely tints of yellow and rose, like petals
of a flower. In some plants, such as the sumac, the bud
scales do not fall but develop into leaves. In the flowering
dogwood the scales of the winter flower buds actually do
develop into what are commonly supposed to be the
petals of a flower. The real flowers are very small and
crowded together in a little head, whereas the four large
white “petals” are the expanded bud scales, their little
purplish-brown tips being the very scales that covered the
bud through the winter. The bud of the tulip tree is a
beautiful illustration of the fact that a bud is an unde-
veloped young branch. There are two outer bud scales
which meet all around at their edges and inclose the rest of
the bud. After the removal of this outer pair, there can
be seen lying against one side a perfect miniature leaf, the
blade folded together and bent forward on the petiole.
Bud scales grow within bud scales and as each pair is re-
moved a similar but successively smaller leaf will be seen.
In the plane tree, or sycamore, there is a single conical

[ 20 ]

FUNDAMENTAL LIFE PROCESSES

bud scale inclosing the remainder of the bud. The scars
from the successive bud scales make the lines that encircle
the twigs of this tree.

There is a bud in the axil of every leaf, but only a few of
them develop in a given season. The others remain dor-
mant. If, however, the leaves are removed from a twig,
some of the dormant buds spring into activity and put
forth leaves. This is how trees defoliated by gypsy moths
or other pests save their lives. The growth of leafy
sprouts along the trunks of trees is due to the develop-
ment of dormant buds, the bases of which have grown each
year just enough to keep them near the surface of the
bark.

To a certain extent trees are able to regulate their foliage
to the amount that is needed. This may be increased by
the development of dormant buds, or decreased by shed-
ding the leaves—an alternative resorted to when, because
of drought, the evaporation is too great for the amount of
soil water available. In the fall in northern regions most
trees drop all their leaves and hibernate until the ap-
proach of spring. In the Tropics or subtropics, where there
is a marked change from wet to dry seasons, many of the
trees drop their leaves in the dry season and remain
dormant until the rains begin again. Trees that drop their
leaves and remain dormant are called deciduous trees;
those that retain their foliage throughout the year are
called evergreen trees. In northern climates the ever-
green trees are chiefly or entirely conifers (pines, spruces,
and the like); but in the Tropics a large proportion of the
arboreal flora is evergreen. However, even in evergreens
the leaves are not everlasting. They have a certain life
cycle, are active for a certain length of time and then die.
In tropical rain-forests new leaves may be constantly
forming as the old ones are constantly dying and being
cast off. Our conifers may retain the leaves for one or
two years or even longer, according to the species.

The leaves of deciduous trees separate from the twig

[21]

THE WORLD OF PLANTS

by a definite line of demarcation, leaving a smooth scar
of a shape characteristic for each species of tree. These
leaf scars, together with the shape and arrangement of the
buds and their characteristic bud scales, and with the
color and surface of twigs, enable the keen-eyed nature
lover to distinguish the trees of his locality in winter as
easily as in summer.

In many herbaceous plants the structure of the vascular
system is simpler than in trees, as the stems live only
during one growing season; but their life processes are
essentially the same. The ‘bundles of conducting tissue
in some are isolated and appear as woody strings. In cer-
tain translucent stems, like those of the sultana and
touch-me-not, one can see the bundles rather distinctly
without cutting the tissue. In some herbaceous stems
they may be so close together as to form a woody ring,
much as in trees. In these there is a cambium layer, and
it is this which enables the stem of the sunflower, for ex-
ample, to increase in diameter.

LEAVES

The leaves of trees have two important functions.
They regulate the evaporation and they manufacture food
for the use of the plant.

The soil water that the roots absorb and the trunk
carries upward, evaporates from the leaves, leaving there
its mineral contents. Under favorable conditions enor-
mous quantities of water are raised from the soil and
passed through the leaves. There is a popular fallacy to
the effect that the sap of a tree flows up in the spring and
down in the fall. As a matter of fact the flow of the soil
water is always up through the young wood and con-
tinues throughout the year except when the tree is frozen.
There is also at the same time a slow current of elaborated
food running downward through the young bark for the
use of the roots, and from one part of the plant to another.

The upward flow of sap is controlled partly by the activ-

[22 ]

FUNDAMENTAL LIFE PROCESSES

ity of the roots and the amount of
water in the soil, partly by the
temperature and humidity of the air,
and partly by the structure of the
leaves. At the most, root pressure
can force the water upward only a
few feet (exceptionally as much as
fifty feet); and the ordinary suction
power of a free tube could not raise
the water more than about thirty
feet, which is the maximum height
water can be raised in a single-valved
suction pump. Just how the water
is drawn or forced up in trees that
reach well above these heights is yet
a subject of controversy among bota-
nists. Some of the giant sequoias and
redwoods, in America, and some of
the species of eucalyptus, in Aus-
tralia, probably grow as tall as
Basitece.

The upward current controlled by
evaporation from the surface of the
leaves is called the transpiration
‘current. To explain the method by
which the leaves accomplish this
partial control of the upward flow of
sap, we must examine the structure
of those organs. The leaves of ordi-
nary deciduous forest trees are flat
and have a complex system of branch-
ing and interlacing veins and ribs.
The main rib, running from base to
apex, isthe midrib: « The’ ribs))are
extensions of branches from the vas-
cular system (wood and bark) of the
twig. They contain the tissues of

[23]

Fic. 10. Branch
standing in glass
tube in a dish of
water draws water
up as it evaporates
from the leaves.
After Holman and
Robbins

THE WORLD OF PLANTS

this vascular system but lack the cambium, hence they
have no power of growth after being fully formed. The
vascular system of the leaf constitutes its framework, and
also serves for the distribution of liquids throughout the
leaf.

Both surfaces of the leaf are covered by an epidermis of
closely arranged cells with no spaces between them (Fig.

Ngee

Leas

‘

°*Saa=

OQ,
files Ea

Fic. 11. Left, section through a green leaf; a veinlet is cut

through near the center; black dots are chlorophyll grains; right,

epidermal cells of a green leaf, showing three breathing pores.
After Smith and Kerner

11, left). Between the two surface or epidermal layers
there are thin-walled cells loosely arranged and with a
varying amount of air space among them. Here and there
among the epidermal cells are the breathing pores (called
stomata, singular stoma). These highly important and
curious structures require some explanation. A breathing
pore consists of two guard cells with a small opening
between them as shown in Figure 11, right. The two
sausage-shaped guard cells are very sensitive to moisture,
absorbing it readily and just as readily giving it up. As
they absorb moisture they lengthen, but, being fixed at
the ends, they are forced apart, and so create a larger

[ 24 ]

FUNDAMENTAL LIFE PROCESSES

space between them. On losing moisture they lie flat
against each other, closing the opening. In other words,
when the air is moist the pores open; when the air is dry
they close. The multitude of stomata, therefore, form an
automatic system controlling evaporation. But the
stomata are not the only means by which water may
escape from the leaf. More or less moisture passes out
directly through the epidermis, the amount depending on
the thickness and composition of the outer cell wall. In
plants of dry climates the epidermis usually contains sub-
stances that resist the passage of water, and most plants
of arid regions possess some device by which to hinder
evaporation and so enable them to endure drought. Such
devices in the leaf include, among many others, hairy
covering, mucilaginous or resinous juice, and fleshy or
woody structure. (See page 79.) However, most of the
moisture passes out of the leaves, except in plants of
uniformly humid regions, through the breathing pores;
hence the loss can be regulated.

It should be noted that the moisture passes from the
leaves in the form of vapor, first from the cells into the
air spaces of the leaf and then through the pores.

The breathing pores are usually confined to the lower
surface of a leaf, or at least are more numerous there.
They are present in large numbers but because of their
small size occupy only a small proportion of the surface.
One author gives the number of stomata per square milli-
meter (a twenty-fifth of an inch, squared) as follows:
Apple, 250 beneath, none above; olive, 625 beneath, none
above; pea, 216 beneath, 101 above; corn (maize), 158
beneath, 94 above. The breathing pores can be detected
with a good hand lens.

Water can not pass into ordinary plants through the
leaves. If plants lose more water than the roots take in,
the leaves wilt. Plants that wilt in the daytime may
revive at night; not, however, because the leaves have
absorbed the dew, but because lessened evaporation in the

[25 ]

THE:- WORLD OF (PLANTS

cooler night air has enabled the roots to catch up in
supplying water.

The second important function of the leaves is that of
manufacturing food for the plant. This process is prob-
ably the most important chemical reaction in the world,
for all animal life is dependent directly or indirectly on
plants for its food. Only plants can convert the inor-
ganic elements into organic food, and plants can do this
only in their green parts, normally the leaves. In the cells
of the leaf is the green coloring matter of plants, the
chlorophyll, in the form of minute granules visible indi-
vidually only with a microscope of considerable magnifica-
_ tion. Within cells containing chlorophyll the living pro-
toplasm is able, in the sunlight, to produce carbohydrates
from carbon dioxide and water. This process is called
photosynthesis (combination by means of light), and
takes place only in the light—actively in bright sunlight,
more slowly in diffused daylight; it stops altogether in
darkness. :

It is probable that the first carbohydrate to be formed is
sugar, but this, being soluble in the cell sap, can not be
seen. The first visible product is starch. The chemical
reaction by which sugar is produced is expressed in its
final form by the equation

6CO, a 6H,O = C.Hi20¢ -- 60,
carbon dioxide water sugar oxygen

The carbon dioxide is a component of the air and enters the
leaves through the breathing pores. It constitutes but a
small portion of the air (by volume three hundredths of
one per cent), but is the basic material from which all life
is derived. Carbon dioxide is one of the products of com-
bustion. For example, when wood burns the oxygen of
the air unites with the carbon of the wood to form carbon
dioxide, which disappears in the smoke. This is the reverse
of what happens in photosynthesis, for as the equation
given above indicates, carbon dioxide is absorbed and

[ 26 |

FUNDAMENTAL LIFE PROCESSES

oxygen is given off in that process. The release of oxygen
during photosynthesis may be observed if water plants are
watched closely in the sunlight: the bubbles of oxygen
can be seen rising through the water. Furthermore, the
intake and the outgo of gas can be tested in a laboratory
by placing a plant under a bell jar; and the amounts of
carbon dioxide used and of oxygen given off can both be
measured.

Sugar, starches, and similar compounds are known
chemically as carbohydrates because they contain only
carbon, hydrogen, and oxygen, with twice as many hydro-
gen atoms as there are oxygen atoms. These carbo-
hydrates, the product of photosynthesis, are the food of
the plant. From them the plant manufactures all the
multitudinous substances that are found in its various
tissues, including the protoplasm itself.

Some DeraiLs or PLanr CHEMISTRY

The mineral elements taken up from the soil by the
plant are incorporated in various ways. The important
element nitrogen, for example, enters from the soil in the
form of nitrates and nitrites. Although nitrogen is plenti-
ful in the air, ordinary plants are unable to make use of it
from that source; they must obtain it from the soil. It is
interesting to note that the soil in its turn does not acquire
this element from the rocks from which soil is formed by
disintegration (for they do not usually contain nitrogen),
but rather from the air and from the action of soil bacteria.
The element is washed out of the air to the earth in the
form of oxides of nitrogen, which are formed by the
action of lightning flashes in forcing nitrogen into com-
bination with oxygen. The high voltage of the electric
flash is sufficient for this purpose.

The action of soil bacteria is the other source of nitrogen
in the soil. Certain kinds of plants, especially legumes
(members of the family Leguminosae, such as peas, beans,
clover, and alfalfa), have small nodules on the roots, within

(27 |

THE WORLD OF PLANTS

which live bacteria. These bacteria have the power of
taking free nitrogen from the air, and converting it into
compounds which can be absorbed and utilized by the
plant. The discovery of this action of bacteria in root
nodules was made only within recent years, though it had
long been known that soil upon which clovers and other
leguminous plants had been grown was richer than other
soils. The age-old practice of crop rotation with clover as
one of the crops was based on this empirical knowledge.
While photosynthesis takes place only in the green
parts of plants, the digestion of the food and the conver-
sion into protoplasm and other substances used by the
plant in its growth may take place in any living cells,
even in the same cells that are engaged in photosynthesis.
These processes (called metabolism) are essentially the
same as the digestive and constructive processes in ani-
mals. Animals take in food already elaborated and use it
for their own living needs; green plants first manufacture
their food from the constituents of the soil and air and
then use this food in much the same manner as do animals.
During metabolism, which involves a slow burning or
oxidation, oxygen is absorbed and carbon dioxide is given
off. This explains why roots die if they are cut off from
an air supply, as they could not then obtain the oxygen
(see page g) necessary for the activity of the living root
cells. Photosynthesis takes place only in the light, but
metabolism takes place in both light and darkness. Dur-
ing photosynthesis the green tissue gives off much more
oxygen than it takes in for use in metabolism, and it is in
general true that plants give off oxygen in the daytime
and carbon dioxide at night. Because of this it has been
suggested that plants should not be allowed in sleeping
rooms at night, especially not in sick chambers. However,
a few plants in a sick room need cause no apprehension,
for the amount of carbon dioxide exhaled is so small in
proportion to the air of the room, and is so quickly dif-
fused, that it has no appreciable effect on the composition

[28 ]

FUNDAMENTAL LIFE PROCESSES

of the air of the room. A person or a lamp or a gas jet
would produce much more carbon dioxide in a room than
would a few house plants.

The walls of plant cells are impermeable to solids, but
allow liquids to pass through by diffusion so that only
liquids can be transported from cell to cell, and from one
part of the plant to another. Minerals taken up by the
roots are in solution in the sap, and food elaborated by the
leaves must also be in solution before it can be carried
to the roots and other parts of the plant for their nourish-
ment. However, plants store quantities of food in the
form of solids because these economize space and resist
decomposition better than do liquids. The potato plant,
for example, manufactures organic material in the leaves,
a part of which accumulates in the form of starch. This
starch is converted into a soluble form—mostly into one
of the sugars—and is transported to the tubers under-
ground, where the sugar is again converted into starch
for storage. Later, when the potato tuber “sprouts,”
the starch is again converted into sugar so that it may
pass into the young shoot. Seeds, such as corn and wheat,
are storehouses for starch until the time of germination,
when the starch is converted into sugar to pass into the
seedling. Carbohydrates are usually stored in the form
of starch. Proteids (nitrogen-containing compounds) are
stored in other forms; the so-called aleurone grains of the
outer layer of the grains of cereals are one of these.

How are the liquids converted into solids and the solids
again converted into liquids? This process takes place
within the plant cells but can be made to take place arti-
fically in the laboratory. While the exact chemical
changes can not be explained in all their detail, it is known
that a substance is present which brings about the con-
version without losing its own identity or decreasing in
amount in the process. Such a substance is called an
enzyme. There is a particular enzyme for each kind of
conversion.

[ 29 |

THE WORLD OF PLANTS

SPECIALIZED PLANTS

A few flowering plants (such as the pondweeds) live
entirely submerged in the water of ponds and streams.
These plants absorb water directly through the leaves as
there can be no evaporation to cause an upward current
from the roots.

Certain other flowering plants are parasites. The
mistletoe grows upon trees, driving a rootlike process

Fic. 12. Dodder parasitic on a hop vine. Cross section shows
protuberances from the dodder penetrating stem of the hop.
After Kerner

into the wood of the host plant. It absorbs sap from the
host but is not entirely parasitic as it has green leaves of
its own and can therefore manufacture food for itself.
The dodder or love vine, on the other hand, is completely
parasitic (Fig. 12). This curious plant is a salmon-colored
twining vine which grows upon weeds and shrubs in the
summer and fall, often covering them with a tangle of

[ 30]

FUNDAMENTAL LIFE PROCESSES

stringlike stems. Such plants absorb all their nourish-
ment from the host plant, to which they attach themselves
by little protuberances that penetrate the stem. Complete
parasites, of course, need no chlorophyll. Certain flower-
ing plants, such as the beechdrops and cancer-root, are
root.parasites, attaching themselves to the roots of their
host; and certain others of similar aspect are saprophytes,
growing on decaying vegetable matter.

Besides the flowering plants to which we have given
attention in preceding paragraphs, there is a world of more
simply organized plants (thallophytes, see page 87),
ranging from the ferns—the most complex—through
mosses, liverworts, lichens, algae, and fungi, to the bac-
teria—the simplest of all. Those who have had no botan-
ical training may not have recognized the simpler organ-
isms as plants. It may be stated that the fundamental
life processes are the same in these as in the higher plants.
If the plant lives entirely submerged in water, it absorbs
nourishment directly from the surrounding medium. If
it is entirely parasitic (as are rusts, smuts, and their like),
it absorbs its nourishment from its host, and, having no
need to manufacture food for itself, it will have no
chlorophyll. If it is saprophytic (living on decayed organic
matter) like mushrooms, it will also lack chlorophyll.
These plants will be more fully described in Chapter VI.

[31]

CHAPTER II
HOW PLANTS SEEK THE EIGET

GreEEN plants must have light or they will die, and the
struggle for existence among them is in part a struggle for
light. This competition is particularly severe in dense
forests where tall trunks support a canopy of leaves. The
lower branches die as the shade increases, leaving tall
pillars with branches only at the top. In tropical rain-
forests, the trees of average height provide a canopy with
here and there a giant overtopping it. Below the canopy
are two or three other layers of vegetation, getting along
with less and less light. Finally, the floor of the forest
may have, because of the diminished light, only a scant
covering.

In general, leaves and stems tend to grow toward and
roots tend to grow away from the light. All growers of
house plants are familiar with the curving of their plants
toward the greatest source of light, a phenomenon which is
mechanically explained by the fact that the side of a stem
or petiole away from the light grows faster than the side
toward the light. The effect of light upon growth is called
heliotropism. It is discussed in detail in Part VII of this
volume.

A curious and efficient disposition of leaves in relation
to light is shown in the basal rosettes of many herbaceous
perennials or biennials, for example, the common mul-
lein, the shepherd’s purse, and the dandelion. The
leaves lie flat on the ground or are more or less ascending.
The peculiarity of rosettes is that the younger and shorter
leaves lie over the spaces between the leaves below them so

[32]

PEATE 7

Wisteria climbing on the porch of a house in Washington.
Photograph by Hitchcock

PLATE 8

A cultivated banyan tree at Honolulu with air roots sent down from
the branches. The roots have been trimmed. Photograph by Hitchcock

HOW PLANTS SEEK THE LIGHT

that a maximum use is made of the light. Arrangements
of leaves by which they fit into a pattern to utilize the
light—whether it be in basal rosettes, on the twigs, or on
any other part of a plant—are called leaf mosaics (Fig. 13).

Climbing plants reach the light at the expense of their
neighbors. Instead of building a strong trunk or stem

Fic. 13. Leaf mosaic. The leaves are so arranged that they
get the greatest amount of light and do not shut off light from
each other. After Kerner

themselves, they utilize the strength of the plants on
which they climb. Woody vines, or lianas, are numerous
in tropical forests, often binding trees together in im-
penetrable tangles. In northern regions lianas, though few,
include the grape, Virginia creeper, bittersweet, and
others. Vines may not be able to get a start beneath the
trees in a dense forest. They generally begin their growth

[33]

THE WORLD OF PLANTS

when the supporting plants are young and grow along
with them except along the edge of a forest or clearing.
In fact a dense tropical forest is in a static condition (a
climax vegetation, according to the ecologist). There can
be no new growth of trees or woody vines until an opening
is made by a hurricane, the fall of an old giant, or by some
other accident.

Plants climb in four ways: By clambering; by means of
rootlets; by twining; by means of tendrils.

Clambering bushes stretch up, over, and through their
support, depending for their rise on rapidity of growth.
Some kinds of blackberries and roses climb in this manner.
These plants are aided in clambering by the retrorse
prickles which prevent the stems from slipping back.

Plants climbing by rootlets represent a stage in which
definite organs for climbing are produced. In nature such
plants use as supports the trunks of trees or cliffs but
under artificial conditions they climb on walls of wood,
brick, or stone. The rootlets are found in large numbers
along the side of the stem next to the support, familiar
examples being the English ivy (Fig. 14, 1) and the poison
ivy. The little roots break through the bark of the stem
at irregular places, a fact which proves them to be roots
and not stems. Roots such as these, which are not a part
of the primary root system but break through the epider-
mis at some other place, are called adventitious roots
(Plate 8). In vines that climb in this way the rootlets
all turn toward the support and the leaves turn toward the
light.

In twining plants the main stem is able to swing in a
circle near its upper end (Fig. 14, 2). It swings freely until
it strikes a support, then winds around this in a spiral.
The mechanism by which twining is accomplished is some-
what complicated. An area on one side of the stem grows
faster than the other side and the growing area at the
same time advances, but just what controls this unequal
growth is not known. The slow sweep of the free end is

[ 34]

HOW PLANTS SEEK THE LIGHT

u ‘i IN NVA

U (tl
i 1: | Y il
OD \ oa

Hes ‘

. 9, Ni ui :

yn ft ' Nal f |

ee
«NOS
Fic. 14. Climbing mechanisms. 1, English ivy, showing adven-
titious climbing roots; 2, morning-glory, climbing by twining;
3, passion flower, bearing twining tendrils; 4, Boston vine, climb-
ing by tendrils that end in clinging disks. After Gray and Kerner

[35]

THE WORLD OF PLANTS

halted when a support is reached, and the contact of the
support stimulates the spiral growth to suit the support.
The twining of stems always takes place in the same
direction in the same species, though some species turn
to the right and some to the left. Moreover, the twining
is independent of light or other surrounding conditions.
Delicate climbers like the morning-glory are unable to
twine around a support of too great a diameter. They
can twine around a thread but not around a post of even
moderate size. If the twining tip encounters a support
too large to encircle, it slides up and passes the support
on the nearer side.

The fourth category of climbing plants possesses highly
specialized twining organs, the tendrils, which may be
modified forms of stems, leaves, or parts of leaves. The
tendril of the grape is a specialized stem—the continua-
tion of the main axis. It is pushed into a lateral position
by the axillary bud, which then takes its place as the main
stem. The tendril is opposite a leaf but has no leaf below
it, and the branches of the tendril come from the axils of
minute bracts which represent leaves. All these facts
show that the grape tendril is a modified stem and not a
leaf. In the garden pea, on the other hand, it is the termi-
nal portion of the compound leaf, including the end of the
axis of the leaf and the uppermost pair of leaflets, which
is developed into a tendril. In the virgin’s-bower (Clem-
atis) the petioles of the leaves twine in one or two spirals.
The greenbrier (Smilax) develops a pair of tendrils near
the base of the leaf.

The movements of tendrils and their branches are the
same as the movements of twining stems. The tips swing
in a circle and twine in a spiral around a small support.
When the tendril of the grape, for example, reaches a
certain age it rather suddenly contracts into a spiral.
If the tendril does not succeed in reaching a support be-
fore this contraction takes place, it forms a single spiral
and is of little use to the plant subsequently. If the end

[ 36 |

HOW PLANTS SEEK THE LIGHT

reaches a support and twines around it, a double spiral
is formed between the grape stem and the support of the
tendril, half of the spiral twining one way and half in the
opposite direction. The double spiral is the result of pure-
ly mechanical conditions. If a rubber band having one
end fixed and the other free is twisted by the fingers the
free end revolves. If both ends are fixed and it is twisted
in the middle, it forms a double spiral as does the tendril.
The coil of a tendril below the point of support (Fig.
14, 3) draws the main stem closer to its support and also
serves as a spring to take up any motion of the plant
caused by wind or other forces.

Certain tendrils produce disks at their extremities by
which they can attach themselves to flat supports (Fig.
14,4). The Virginia creeper climbs in this way as does the
Japanese creeper or Boston vine (4mpelopsis Veitchet) so
common on the walls of houses in the eastern cities of the
United States.

CHAPTER III
HOW PLANTS REPRODUCE

So far we have considered the plant as it lives from day to
day. In time it must succumb either to accident or to old
age, though the duration of the individual body varies
widely, depending on a number of conditions. As in
animals, nature has provided for a continuation of the
species by means of reproduction. The simplest plants—
the bacteria and one-celled algae, for example—repro-
duce by division of one cell into two, each cell growing to
full size, when it in its turn divides, and so on. In some
bacteria this division takes place as often as once in
twenty minutes. Such division is similar to growth, in
which cells divide but remain attached. The active part
of yeast is a minute one-celled plant in which the cells are
formed by budding, that is, by a bulging out of one side
of the cell until the new plant is as large as the old. The
single cell soon forms a colony of loosely aggregated cells,
which are easily separated. In a filamentous alga there
may be a single row of cells. As the cells divide they re-
main attached, end to end, and the filament increases in
length. In ordinary higher plants cell division is the basis |
of growth, but it takes place in two or three directions,
forming a solid tissue.

Commonly, however, even in the lower plants there are
special bodies or organs that reproduce the plant. In the
lower plants these bodies are called spores; in the higher,
seeds.

The phenomenon of sexuality in animals is, of course,
well known to all. The individual animal is male or

[38]

HOW PLANTS REPRODUCE

female, and through the fertilization of the female by the
male a new individual, the offspring, is formed. The
process of fertilization (the union of two bodies of proto-
plasm to form a single body) in plants is fundamentally
the same as in animals. The simplest kind of fertilization
is illustrated by certain filamentous algae. In these the
walls of the cells of two adjacent filaments bulge out to
produce tubes which meet and form a continuous passage.
Through this the protoplasmic contents of one cell pass
into the other and the united contents form a ball with a
thick cell wall. This new body is a spore, often called a
resting spore, because when the filament disintegrates
owing to freezing or drying up of the water of the pond in
which it grew, the spore sinks to the bottom and remains
dormant until the return of favorable conditions when it
germinates, thus forming a new individual.

In the alga we have been discussing there appears to be
no difference between the two cells that unite. But
physiologically the cell which receives the protoplasm is
the female cell and the one which gives, or fertilizes, is
the male cell. In all except the lowest forms of life there
is a distinct difference in appearance between the cells of
the two sexes. In some algae the male cell is able to swim
to the female cell, probably attracted by some chemical
emanating from the latter. The methods of fertilization
observed in the fungi and algae are of great variety and of
absorbing interest.

Besides the sexually formed spores, the fungi and algae
often produce spores without fertilization, that is, asexu-
ally. Asexual spores often serve for the immediate and
quick spread of the species, while the sexually formed
spores are more likely to be resistant bodies that carry the
species through unfavorable seasons or conditions.

The spores of many fungi, such as bread mold, are fa-
miliar to every one. Bread mold produces a tangled mass
of very fine threads (the mycelium) which is the body of
the fungus (Fig. 15). In time small black dots can be

[39]

THE WORLD’ OF PLANES

seen scattered over the mass. These dots are little cases
full of minute spores so light that they are wafted through
the air to alight on other pieces of bread, where they
germinate. The com-
mon blue mold of
fruits,, bread, and
vegetables forms min-
ute tufts of spores; the
parts of wheat rust
that are visible to
the naked eye on the
leaves and stems of
grain are the spores—
spots or lines of red
or black; the ugly
mass of black powder
typical of corn smut
is made up of count-

ies

¢
te

i>
See

CIR OAL less myriads of
se : spores; finally, mush-
The IS MAN rooms, toadstools,
$A) puffballs, bracket

Fic. 15. A mold, showing the branch-
ing of the filaments; the upright
organs bear minute spore cases. The
small figure shows a spore case of

fungi, and so on, are
all spore holders—
the visible parts of
fungi whose filaments

bread mold containing spores; much

enlarged. After Goebel penetrate decaying

wood and rich soil,
this part being known as the mycelium (see page 40).

The spores of mosses are borne in the little capsules at
the summit of the stems, whereas the spores of ferns are
found for the most part in spots or lines on the backs of
the leaves or fronds (Plate 17).

The reproductive bodies of flowering plants are the
seeds, which are infant plants all ready to grow into
individuals like their parents. If an apple seed or a bean
or a peanut is opened, it will be seen to consist of two

[ 40 ]

PLATE

The floral parts of a lily (Lilium washingtonianum). The six colored leaves

include three outer sepals and three inner petals. Within are six stamens

each bearing an anther. In the center is the pistil, of which the style,

bearing the stigma, protrudes beyond the stamens; the ovary is hidden in
the base of the flower. By F. A. Walpole

HOW PLANTS REPRODUCE

thick little leaves with a bud between them. Here is the
whole plant in miniature; for the bud, called the plumule,
is a little stem, which develops leaves above and roots
below. All seeds are produced by flowers. Incidentally,
though acorns and walnuts are known to be seeds, it may
surprise some to learn that oaks and walnut trees have
flowers.

The flower consists of a highly specialized branch with
leaves, and is wholly consecrated to the service of the
next generation. A large, relatively simple flower like
the lily will serve to illustrate the parts (Plate 9). There
is on the outside a showy set of six parts in two series of
three each. The outer series is the calyx, made up of
sepals; the inner series is the corolla, made up of petals.
Within these parts lie the six stamens, each consisting of
a slender stalk (the filament) on which rests the two-celled
anther, which in turn incloses a yellow powder, the pollen.
In the center of the flower is the pistil, consisting of the
enlarged base (the ovary), a rather slender stalk (the
style) and a broadened tip (the stigma). Within the
ovary are the little ovules which later become seeds. In
the flowers of other plants the shape, size, and number of
the parts may show great variation from those of the lily.
The rose, for example, has a green calyx, a white, red, or
yellow corolla, and numerous stamens and pistils.

The process of fertilization in flowers merits descrip-
tion. When the anther is mature it breaks open, releasing
the pollen which consists of a fine, usually yellow, powder,
the grains of which are barely visible to the naked eye.
By various means (to be described later), the pollen is
transferred to the stigma. When the stigma is mature—
that is, ready to receive pollen—the surface is usually
sticky or hairy so that the grains of pollen adhere to it.
The grains now germinate by sending out a slender tube
much like a root hair. This pollen tube grows down into
the tissue of the stigma, through the style and into the
ovary. The tube seems to be led through the tissue by

[41 ]

THE WORLD OF PLANTS

the attractive force of a chemical in the cells through
which it passes. Within each ovule is a single cell—the
egg cell—whose function is to be fertilized, that is, to
receive the pollen. The pollen tube finally grows through
a small opening in the ovule and reaches the egg cell. The
contents of the pollen tube, which have kept close to the
growing end, fuse with the contents of the egg cell. This
process is fertilization. One pollen tube fertilizes one
ovule and only one. [If fertilization of all the ovules is
to take place, there must be as many pollen tubes as there
are ovules.

After fertilization the egg cell divides and subdivides,
that is, commences to grow, and finally forms a small
plant. Thus the ovule is converted into a seed but remains
within the pistil which meantime has undergone change
and has become the fruit. In most seeds there is a cessa-
tion of growth after a certain period, and then the seed
and fruit are said to be ripe. The seed actually consists
of the small plant (the embryo) and, either within the
embryo or surrounding it, a quantity of nourishment to
support it during its further growth (germination). The
whole is surrounded by the seed coat. The embryo is
plainly visible in some seeds, such as those of the morning-
glory and the maple, and the crumpled seed leaves may
be green and all ready to start growth anew. In other
seeds the embryo is a mere speck embedded in the nour-
ishment. Thus the grain of corn shows a small straight
embryo (germ) at one side of the lower end. In the peanut
the embryo occupies all the space within the seed, and
consists of the two large seed leaves (cotyledons), lying
face to face, the small stem from the end of which in
germination the root grows, and a pair of small leaves
(the plumule) from between which the shoot grows.

The major part of the nourishment stored in the seed
is commonly starch, as in our grains, beans, and peas.
Oil is stored in the castor bean and in all oily seeds. There
is some oil in the corn kernel. Proteids (compounds con-

[ 42]

HOW PLANTS REPRODUCE

taining nitrogen) are also present, especially in the bean
and its allies. The gluten of wheat is a proteid. Many
seed coats are very hard and resistant; for example, in
the honey-locust, in various sea beans that are washed
up on southern shores, and even in the apple. This hard
seed coat prevents the loss of water by the seed and also
prevents the premature absorption of water.

Pistils with one ovule form one-seeded fruits that may
have the aspect of a seed. The sunflower and all the
other Compositae—the family to which it belongs—have
so-called “‘seeds,” which are in reality one-seeded fruits.
Where there is any difficulty in distinguishing between
fruit and seed, opening the questionable object provides
a simple way out. If it is a fruit, the seed will be found
loose on the inside, wrapped in its own thin coat; if a seed,
the seed coat will prove to be grown tight to the contents.
This distinction breaks down in grains (wheat, maize, and
the like), because in them the seed is grown fast to the
wall of the fruit.

POLLINATION

The methods by which the pollen of the flower reaches
the stigma are varied and curious and not always as simple
as one might suppose. In some flowers the anthers are in
close proximity to the stigma and the pollen comes in
immediate contact with the stigma of the same flower.
Such flowers are said to be self-pollinated. If one takes
the trouble to examine the flowers in his own vicinity he
will notice at once that commonly there is no such prox-
imity of anther and stigma. In fact, most flowers are so
constructed that self-pollination is impossible or difficult
or, at least, less likely than cross-pollination in which the
pollen of one flower fertilizes the stigma of another.
Charles Darwin noticed this condition and asked himself
why it existed. “Why does nature so commonly appear
to abhor self-pollination?’ He inaugurated a series of
experiments to find out the effect of self-pollination as

[ 43 ]

THE WORLD OF PLANTS

compared with cross-pollination, using several species of
plants in parallel tests—half the plants of each species
being self-pollinated by hand, the other half being
cross-pollinated. In nearly all the tests the cross-polli-
nated plants produced more and better seeds. Further-
more, the plants raised from cross-pollinated seed were
usually more vigorous than those from self-pollinated
seed.

On the whole, cross-pollination, that is, having two
distinct individuals as parents, is an advantage to the
offspring. Only a few of the numerous and curious devices
by which cross-pollination is brought about can be re-
ferred to here, but the reader will find it exceedingly
interesting to examine the flowers of his vicinity and de-
termine the methods used.

The pollen of a few flowers is transported by water, but
wind and insects (sometimes humming birds), are the
transporting agencies employed by most flowers. The
tape grass furnishes a striking example of the use of water
currents to effect pollination (Fig. 16). The plants are
diecious. The staminate flower-buds, before expanding,
break away from their pedicels and float on the surface;
there they expand and shed their pollen around the pis-
tillate flowers which are sent to the surface at the same
time. After pollination the stalk of the pistillate flower
coils in a spiral, drawing the flower under water to ripen
its seeds.

Plants adapted to wind pollination produce vast quan-
tities of dry pollen—thousands of times as many pollen
grains as there are ovules to be fertilized; for wind is a
wasteful distributor. Wind-pollinated flowers are usually
inconspicuous and in many trees and shrubs they make
their appearance before the leaves which would interfere
with the flying pollen. The elms, ashes, and some of the
maples, the spicebush, alder, and hazelnut bloom while
the trees are still bare of leaves. In many of the wind-
pollinated plants, especially trees and shrubs the flowers,

[44 |

HOW PLANTS REPRODUCE

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THE WORLD’ OF ‘PLANTS

are unisexual; that is, the stamens and pistils are borne
in separate flowers, either on the same plant—as in the
sedges (Carex), maize, oaks, and hickories—or on separate
plants—as in the willows and poplars. In the oaks,
hickories, birches, and alders the staminate flowers are
numerous on a flexible axis, forming catkins from which
the pollen is easily shaken out by the wind; but they grow
below the few pistillate flowers, which are set close to the
twigs, so the pollen will not fall on these flowers.

Even when flowers are perfect—that is, have both
stamens and pistils—as in the lily, there is usually some
structure or characteristic which facilitates cross-pollina-
tion. There are two general characteristics of this nature
found in both wind- and insect-pollinated plants. The
first is described as the “‘prepotency of foreign pollen,”
which means that when foreign pollen and pollen from the
same plant fall upon a given stigma, the foreign pollen

“takes” quicker—that is, grows faster down through the
style of the ovule. The other characteristic is that in a
given flower the anthers do not mature at the same time
that the stigma is receptive. If the stigma is receptive
first it must be fertilized from another flower. If the
anthers mature first most of the pollen is removed from
them before the stigma matures.

Plants adapted to insect pollination produce far less
pollen than do those adapted to wind pollination, and
many pollen grains are sticky—in some plants, such as
orchids and milkweeds, so sticky that they adhere in
masses. The most highly specialized devices to bring
about cross-fertilization are to be found in insect-polli-
nated flowers.

Such flowers usually have showy corollas, for example,
the roses, petunias, and morning-glories; or if the flowers
are small they are massed in showy heads, as in red clover,
yarrow, or wild carrot; or if the flowers themselves are
inconspicuous they may be surrounded by showy bracts,
as in the flowering dogwoods, snow-on-the-mountain, and

[ 46 |

HOW PLANTS REPRODUCE

poinsettia. The calla or calla lily is a striking example of
inconspicuous flowers in a showy bract, for the “lily” is
a spathe surrounding the minute true flowers, which are
borne on a club-shaped axis. his showiness is thought
to be a guide to insects. But whether it is or not, what
really draws insects to flowers is either pollen or nectar.
Also, many flowers have an odor which attracts insects.
This odor may be agreeable (to the nostrils of man) and
attractive to moths, butterflies, and some other insects, or,
as in the carrion-flower and skunk-cabbage, it may be
disagreeable to man and attractive to flies and beetles.

In flowers adapted to insect fertilization, the stamens
and stigmas are so arranged that when the insects visit
the blossoms for nectar the anthers come in contact with
a certain part of the insect’s body, dusting it with pollen
which is scraped off on the stigma of the next flower
visited before the anthers are reached.

As there are multitudes of insects and multitudes of
flowers the devices which result in cross-pollination are
almost infinite. The common sage (Fig. 17) is adapted
to pollination by bumblebees. On entering a flower for
nectar the insect hits the lower part of the stamen lever
and brings the anther down on her back. At this time the
stigma is not mature and remains in the upper lobe of the
flower. Later the stigma opens and curves down to a
position where it will rub against a visiting bee and so pick
up pollen from her back.

The pollination of the lady’s-slipper, or moccasin
flower (Cypripedium acaule), is shown in Figure 18. When
a bumblebee visits the flower she falls into the slipper, as
indicated in the first drawing. She sips the nectar among
the hairs near the stigma and finally makes her escape in
the only way possible—that is, through the opening at
the base of the flower. On her way she is forced to pass
first the stigma, which scrapes pollen from her back, and
then the anthers, which rub against her back and give her
a new supply of pollen for the next flower.

[ 47 |

THE WORLD OF PLANTS

—~
YY =—

Fic. 17. Pollination of the sage by a bumblebee. Upper,
bumblebee entering a flower, the stigma of which (above) 1s
immature, and striking the lower branch of the anther, which
brings the upper branch down on its back; center, bee entering
another flower, in which the mature stigma (the lobes spread
apart) scrapes off pollen from the bee’s back (this flower has
already shed its pollen); below, diagrams showing the structure
of the stamen. After Gibson

[ 48 |

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r “co > » fo S = =I SIDMOT,
SUIUTEYS pue ‘steqjad ‘spedas AUPBU Sey JOMOY You's SNYIBD Sulq WITS e ‘snaJja5 SULWIOOTG yYystu jo SIO M( IH

Ol ALVId

PE AGE i

Yucca growing on Mount Wilson, California. The flowers are pollinated
by the yucca moth. Courtesy of Ferdinand Ellerman

HOW PLANTS REPRODUCE

Fic. 18. Pollination of the lady’s-slipper. 1, bee entering the

sac; 2-3, in the sac, feeding on the nectar; 4, rubbing its back

(covered with pollen from another flower) against the stigma;

5, getting a new supply of pollen from the anther on its way out.
After Gibson

[ 49 |

THE WORLD OF PLANTS

The pollination of the yucca (Fig. 19) is one of the most
remarkable in the vegetable kingdom, because it involves
the exercise by the insect of an instinct that appears like
reason. The yucca flower
is built on the plan of
the lilies—it is bell-
shaped and has six divi-
sions of the perianth,
six stamens, and a stigma
with three short branches.
The yucca moth is rather
small, scarcely as long as
the ovary of the flower
in which she lays her
eggs.) he: ¢omnbss vor
larvae, of the moth feed
on the ripening seeds.
The flowers can not be
pollinated except by the
aid of this moth. If the
moths are kept out by a
covering of gauze, no
seeds develop; nor do
they if the yucca is grown
in gardens where the moth
does not occur. The moth
lays her eggs in no other
plant. Hence the plant
Fic. 19. Pollination of the yucca. is dependent on the moth

One of the flowers is cut open to for its pollination and the

show the moth planting pollen in formation of seed, and
the depression between the stig- :
miei: AdtoruK cance the moth is dependent on

the plant for nourishment
for her larvae—an absolute interdependence. But
the most wonderful part of the relation is yet to be
told. Before laying her eggs, the moth visits a fower and
gathers a mass of pollen which she holds in a ball under her

[50]

HOW PLANTS REPRODUCE

“chin,” that is, below her head. She then flies to another
flower where she lays her eggs in the ovary. Immediately
after this she crawls up to the stigma and, taking some of
the pollen from its store, places it in the forks of the three
branches of the stigma and rams it down tight. She may
repeat this process more than once. Ordinarily only
about a third of the seeds in a capsule are destroyed by
the larvae. Of course, if all were destroyed the moth
would exterminate the yucca and defeat her own ends.

There are many cases of interdependence between cer-
tain species of plants and certain insects, the flower hav-
ing become modified to such an extent that only one
species of insect can reach the nectary and in doing so
pollinate the stigma. As in such combinations, one species
of insect has a monopoly on one species of plant, the
insect depends on the plant for its food—that is, nectar.
In such situations, common among orchids, the plant
and the insect must inhabit the same region. There is
reason to believe that there have been instances where
the extinction of the insect has brought about the extinc-
tion of the plant, or the reverse.

There are all gradations between such highly specialized
flowers adapted to one kind of insect and simple open
flowers, like those of the buttercup, where many kinds of
insects can get nectar. The flowers of a large number of
plant species are able to use their own pollen in self-
pollination in case cross-pollination fails. Thus the wheat
flower is open for cross-pollination only about fifteen
minutes, but will self-pollinate after the flower closes if
cross-pollination has failed.

The plans of nature are sometimes circumvented; or
possibly we might say that two plans sometimes conflict.
Certain large tubular or bell-shaped flowers, like those of
the trumpet creeper (Tecoma), secrete considerable nectar
at the base of the corolla. Such flowers are usually polli-
nated by long-tongued moths or butterflies or by hum-
ming birds. Now the carpenter bee has learned to bite

[51]

THE WORLD OF PLANTS

through the corolla near its base and pilfer the nectar, and
the holes sometimes seen in these long corollas bear evi-
dence of the work of these insect thieves.

The various methods of pollination and the devices to
secure cross-fertilization have an important bearing on
horticulture. For instance, the grower of strawberries
knows that certain varieties of this fruit are pistillate only.
Although the wild strawberries have perfect flowers, there
are several cultivated varieties in which the stamens are
reduced in number or are abortive. The planting of such
varieties by themselves would be futile because the
flowers would not be pollinated, and so no fruit would be
produced. The grower, therefore, plants at intervals
rows of some other variety that produces plenty of pollen.
Insects—most of them honey bees—transport the pollen.

Growers of orchard fruits have found it to their ad-
vantage to have colonies of honey bees nearby, especially
when the orchards are large, for otherwise there might
not be a sufficient number of insects to pollinate the
flowers.

Some forty years ago the failure of a certain orchard to
bear fruit brought out an interesting fact not previously
known. A grower decided to set out a commercial orchard
of Bartlett pears on a large scale. When the orchard came
to maturity he was much disappointed to find that, though
the trees blossomed freely, they produced only a few
fruits. Incidentally, the mystery was increased by the
fact that what fruit was produced was confined to the trees
along the edges of the orchard. An investigator from the
United States Department of Agriculture studied the case
and found that the Bartlett pear was self-sterile, that is,
the flowers could not be fertilized by their own pollen.
As all Bartlett pear trees have been produced by grafts
from one original tree they are essentially parts of a
single individual. Consequently, if one tree was self-
sterile with its own pollen it would likewise be sterile
with the pollen of the other trees of the same variety.

[52]

HOW PLANTS REPRODUCE

The few fruits produced at the edges of the orchard were
the result of chance fertilization by pollen of other pear
varieties carried from a distance by bees. The problem
was solved by grafting other varieties of pears at intervals
in the orchard and by keeping bees to transport the pollen.
It has since been found that several other varieties, not
only of pears but of other fruits, including the Winesap
and Delicious apples, the Burbank and Wildgoose plums,
the Napoleon cherry, and the J. H. Hale peach, are self-
sterile or too nearly so to be grown profitably without
planting other varieties nearby to supply pollen for cross-
fertilization.

Horticulturists have learned to use cross-fertilization
to produce new varieties of plants artificially. Strictly
speaking, fertilization between two varieties results in a
cross; and fertilization between two distinct species re-
sults in a hybrid. The terms are not always carefully
distinguished. The mechanical part of the process of
producing a cross or a hybrid necessitates transfer of the
pollen by hand from the anthers of one plant to the stigmas
of another. Meantime the stigma to be fertilized must be
protected against pollination from its own flower or from
any outside source. Usually the stamens are removed
before maturity from the flower to be fertilized, and the
emasculated flower is protected by bags or by some other
means from being reached by foreign pollen. In recent
years large numbers of desirable new varieties of orchids,
irises, narcissuses, roses, orchard and small fruits, grains,
and many other plants useful to man have been originated
by crossing and hybridization. It should be understood,
however, that not all crosses are better than the parents.
Only a few individuals out of the large number produced
by numerous trials will show superior characters and be
worthy of further attention.

When a cross combining the desired characters of the
two parents is obtained it is propagated by vegetative
means, if this is possible, thus insuring the uniformity

[53 ]

THE WORLD OF ‘PLANTS

(under like conditions) of all the plants. Annuals, of
course, may usually be propagated only through the seed.
It is then necessary to examine the progeny and select for
further propagation only those that show the favorable
characters of the parent. Growers of annual plants for
commercial purposes are constantly selecting to keep the
variety pure and in accordance with the type desired.
The seed is a device for spreading a species through
time and space; it is a living plant in a dormant or resting
state during which there is time for its dissemination. A
few plants, such as the common mangrove of tropical sea-
shores, have no such period of rest. In them the embryo
continues to grow while the seed is attached to the tree.
It throws out a thick heavy root, the young plant falls
from the tree and strikes root in the mud. In plants
whose seeds are dormant for a time, the length of the
period of rest differs greatly between species. In the
soft or silver maple (cer saccharinum) the seeds germi-
nate within a few days after ripening. But even in this
short time their large wings may carry them a long dis-
tance with the aid of the spring gales. The seeds of the
sugar maple (4. saccharum), on the other hand, do not
germinate until autumn. Seeds of the wildrice (Zzzania)
will not germinate if they once become dry. Some seeds
require a long period of rest and can not be forced to
germinate before their time; some require a period of low
temperature treatment. A knowledge of the peculiarities
of seeds in this respect is necessary to the plant grower.
Some seeds retain their vitality for only a single season
and others retain it for many years. Many experiments
have been tried to test the viability of various kinds of
seeds according to age, and one author found that a few
seeds of three species of legumes would germinate eighty
years after the time of their production. Judging from
the rate at which long-lived seeds lose their viability, it is
thought that the extreme probable limit of viability of
any kind of seed is between 150 and 250 years. Stories

[54]

HOW PLANTS REPRODUCE

of the germination of seeds taken from ancient tombs may
be classed as myths or as based upon the trickery of
guides or workmen.

DISPERSAL OF SEEDS

The numerous and curious devices by which cross-
fertilization is secured are matched in interest by the

Fic. 20. Contrivances for throwing seed. Left, violet pods, whose

sudden opening pinches out the seeds; right, bean pods, in

which sudden coiling of the two halves scatters the seeds.
After Kerner

adaptations which effect the dispersal of seeds. Seeds are
scattered by four principal means: by contrivances which
shoot the seed to a distance, by wind, by water, and by
animals. In propulsive contrivances a tension is set up
in the ripening pod which finally produces an explosion,
scattering the seed. The snapweed or touch-me-not 1s an
amusing example. Violet pods suddenly and violently
split into three parts throwing the seed to a distance of
several feet (Fig. 20). The capsule of witch-hazel pinches

[55]

THE WORLD OFVPEANTS

out its two black seeds with such force as to send them
twenty feet or more away. Many bean pods open by a
sudden coiling of the two halves. The tropical sandbox
tree has large woody pods, which explode with great
violence, throwing out hard lens-shaped seeds half an
inch in diameter, thereby endangering passers-by.

Just as many flowers rely on the wind to transport
their pollen to receptive stigmas, so many plants depend on
the same ubiquitous agency to scatter their seeds. Small
seeds are carried long distances by the wind without
special adaptations. In northern countries the migra-
tions of late-maturing seeds are often aided by crust on
the surface of snow over which they are borne with sur-
prising velocity. In open country, plains, and prairies,
tumbleweeds break away and roll before the wind, scat-
tering their seeds as they go. The Russian thistle (which
is really not a thistle, but a relation of the pigweed), an
introduced annual now common in the northern part of
the Great Plains, breaks off near the surface of the ground.
The branches are light and stiff and the plant as a whole
is globular in outline. These tumbleweeds roll across the
plains in vast numbers, and have even been seen to chase
an express train as they are carried along in the rush of
wind behind the rear car. The light branching panicles
of tickle grass and old witch grass break away and travel
in the same way. Great piles of tumbleweeds may gather
in windrows along fences and other obstructions.

Some fruits, such as those of the elm, maple, and ash,
are winged (Fig. 21). The very thin pod of the redbud
and the bract on the stem of the little fruit of the linden
serve as wings; and the thin seed of the catalpa is sur-
rounded by a light wing. Winged fruits and seeds are
more common to trees, from which they get a good start
for their aerial voyages, than to herbs. But a vast number
of fruits and seeds of both trees and herbs have tufts or
tails of woolly or silky hairs. The willows and poplars,
the clematis or virgin’s-bower, milkweeds, willow herbs,

[ 56]

HOW PLANTS REPRODUCE

dandelions, lettuces, and thistles are all carried on the
wind by such devices.

Some fruits, such as those of the balloonvine, bladder-
nut, and groundcherry, are carried in little balloons that
roll before the wind.

Water is the means of dispersal for many plants that
live in or near it. In order to take advantage of water

Fic. 21. Dispersal of seeds by wind. 1, fruit cluster of bass-
wood with winged supporting bract; 2, winged fruit of the maple;
3, cotton, which has hairs attached to the seeds; 4, dandelion,
whose fruits bear parachutelike tufts of hair. After Kerner

currents the fruits or seeds must be able to float, must re-
main uninjured by the water, and must be capable of
germinating and establishing themselves in the situations
in which they are deposited. To secure sufficient lightness
the surrounding tissues are in many cases spongy or
bladdery. Strand plants (plants of sandy seashores) are
distributed largely by ocean currents; this agency may
carry seeds great distances, even thousands of miles (see
page 85).

Some of the most interesting adaptations for dispersal
are found in fruits scattered largely through the agency of
animals. The sandbur (Cenchrus), cocklebur (Xanthium),
Spanish needles (Bidens), stickseeds, and a host of other
plants bear appendanges by which they are easily attached
to the hair or fur (Fig. 22). This method of stealing rides
is a favorite one with weeds such as are common in old

[57]

THE WORLD OF PLANTS

fields and weedy waysides. A walk through lowland
woods or meadows in the autumn is sure to result in a fine
collection of such fruits on the clothing. The seeds of rib
grass, or plantain, are mucilagi-
nous when wet and stick to
animals or even to dry leaves;
in the latter event they. Jane
carried by the wind.

Fleshy and juicy fruits do not
steal transportation but pay their
way handsomely, for nearly all
of them are eaten by some kind
of bird or beast. The smaller

Fic. 22. Fruitofthe fruits are eaten entire and the
burdock. Thehooked seeds pass through the digestive
bracts of the bur .
catch on the hair of tract--unharmed because of their
animale. After simapervious scedcodc— aude akc
Ganong dropped at a distance, some-
times of miles, from the place
where they were eaten. The brambles and redcedar
so common along fencerows were planted by birds
as they sat on the fence. Incidentally, birds are to dis-
persal of plants almost what insects are to cross-fertiliza-
tion. Nuts and acorns are buried in the earth by squirrels,
chipmunks, and other rodents, and the greater number
are left there.

We must not forget that man is a part of nature and
has been for ages. In his migrations he has unintention-
ally carried with him from one place to another a vast
number of plants not cultivated—weeds like weedy
bromes, dandelions, and many others. But, far more
important, he has also taken along with him the seeds of
those plants we are pleased to call cultivated, and he has
scattered these seeds far and wide through the channels
of commerce.

The observer who finds pleasure in wandering through
fields and woods may find much amusement and interest

[58 |

HOW PLANTS REPRODUCE

in studying the methods of seed dispersal in the plants of
his vicinity. He will note many curious adaptations, for
strange and curious things need not be sought in foreign

parts; they are all
about for those who
have eyes to see.

GERMINATION
OF SEEDS

When seeds are
surrounded by the
proper conditions
they germinate, that
is, ‘the embryo re-
sumes its growth.
Whe “first )‘stage* im
this process is the
absorption of mois-
ture. Through the
action of enzymes the
nourishment stored in
the seed (either a-
round the embryo or
in’) its’ \ ‘thickened
cotyledons), is con-
verted into a liquid
form and is absorbed
by the growing em-
bryo. The first visible
change is usually the
protrusion of the
primary root, which
may grow to con-
siderable length and

be covered with root

Fic. 23. Corn or maize. Cross and

longitudinal sections of a grain, an

embryo removed, and two stages of
the germination. After Gray

hairs (see page 5) before any leaves appear.
There are two main classes of embryos: those with one

L591]

THE WORLD OF PLANTS

seed leaf (monocotyledons), and those with two seed
leaves (dicotyledons). The maize, or Indian corn (Fig.
23), is an example of the first group. The embryo of this
plant can easily be seen by cutting longitudinally through
the middle of the grain or kernel. During germination
the seed leaf, or cotyledon, remains within the seed coat,
but the first growing leaf elongates and breaks out of the
seed coat though its tip remains closed over the other
leaves within. If the seed is covered with earth this first
growing leaf pushes through the particles without damage
until it reaches the surface; then the next leaf breaks
through, soon turns green, and the plantlet is established.
If the grain of corn is buried too deeply the little leaf, or
protecting sheath, can not reach the surface; if the grain
lies on the surface the protecting leaf bursts very soon
after emerging from the seed coat and lets out the other
leaves. Not all monocotyledons germinate in the way
described, but this way is characteristic of the grasses.

There are three general types of germination among the
dicotyledons: In one type, the cotyledons remain in the
seed coat; in a second they emerge, but function only as
storehouses for plant food; in a third, they may spread out
and function as foliage leaves.

The garden pea illustrates the type in which the coty-
ledons (the two halves of the pea) remain in the seed coat
(Fig. 24,center). Soon after the root pushes out, the little
bud (plumule) between the two cotyledons grows toward
the surface (if the seed is covered by soil); but the growing
part is bent just below the tip so that it is not the tender
growing summit which is forcing the soil particles aside
but a little bend in the stem. When the surface is reached
the tip straightens out and spreads its leaves. The oak is
another example of this same type (Fig. 24, right); the
fat cotyledons of the acorn remain in the shell while the
root and stem protrude.

The garden bean furnishes an example of the second
type of germination (Fig. 24, left). The little stem

[ 60 |

HOW PLANTS REPRODUCE

between the two thick cotyledons sends out a root at the
lower end and elongates above. If the seed is covered by
soil the upper end forms a bend, backs up, and draws the
cotyledons out of the seed coat. Thus it is not the cotyle-
dons which first appear above the surface, but this bend.
As soon as the cotyledons are drawn out (leaving the seed

Fic. 24. Left, seed (embryo) from which the seed coat has been

removed, and two stages of the germination of the garden bean;

center, embryo and seedling of the garden pea; right, section of
acorn and a seedling of the oak. After Gray

coat in the ground) the stem straightens, the cotyledons
spread but do not grow, and the second pair of leaves
spread rapidly, grow much longer, and turn green; the
young plant is thus established.

In the great majority of dicotyledonous plants the third
type of germination prevails. This differs from the second
type only in that the cotyledons enlarge, turn green, and

[ 61 |

THE WORLD OF PLANTS

function as leaves, though they are usually different in
shape from the leaves that follow. If buried in the soil
the cotyledons are drawn out of the ground by a bend in
the stem, leaving the seed coat in the ground. Germina-
tion in the morning-glory and in the maple is of this type
(Fig. 25).

The bending that occurs in stems of all types of di-
cotyledons when the seed is below the soil surface would

Fic. 25. Germination of the red maple. The winged fruit with

the seed in one end, the seed cut through exposing the embryo,

the embryo removed, the embryo unfolded, and the seedling in
three stages of growth. After Gray

appear to be due to a sort of uncanny instinct; as a matter
of fact it is merely the result of growth that takes place
below the summit. If the seed is above ground, the growth
of the stem pushes the tip forward and there is no bend;
if below ground, the tip can not be pushed through the
soil; as a result the stem forms a loop and so pulls it out.
The seeds of the pumpkin, squash, watermelon, and
others of the gourd family overcome a difficulty in germ1-

[ 62 |

HOW PLANTS REPRODUCE

nating in a way that suggests intelligence. The seed coat
splits a little at the pointed end as the root pushes out.
But the expanse of the firm coat in these large flat seeds
is great in proportion to the plantlet within, and the coat
presses on the cotyledons so hard that they could not
emerge were it not for an unusual contrivance. The young
stem forms a shoulder just under one cotyledon; this
shoulder grips one side of the seed coat and holds fast
while the stem above elongates, pulling the cotyledons
from the firm seed coat. In effect the embryo seizes one
jaw of the firm seed coat and pushes the mouth open while
the cotyledons are drawn out.

It is common knowledge that the root of a seedling
grows downward and the stem upward when the seed
germinates, and that plants in general send their roots
down and their stems up. What causes this growth in
opposite directions? It has been shown experimentally
that the cause is gravity. If seeds are germinated on a
vertically revolving wheel, turning slowly, gravity is
neutralized and the roots and stem grow in the directions
in which they emerge from the seed. If the wheel revolves
rapidly, the roots grow away from the center of the wheel
and the stems toward the center. Centrifugal force has
been substituted for gravity. This response is called
geotropism.

VEGETATIVE PROPAGATION

Whereas seeds—the offspring usually of two parents—
perpetuate the species, many plants perpetuate them-
selves individually by vegetative means. Seeds spread
the species far and wide; vegetative reproduction enables
an individual to occupy adjacent territory quickly. All
vegetative reproduction is the division of an individual
into two or more individuals. The progeny are all parts
of the original plant and possess the same characteristics,
just as the branches of one side of a tree are similar to
those of the opposite side. The different trees of the Ben

[ 63 ]

THE WORLD OF PLANTS

Davis apple are as much alike (barring the effects of
climate and other environmental factors) as are the dif-
ferent branches of the original tree from which they all
sprang. But different varieties of the apple show distinct
differences, though they may all belong to the same
svecies.

Plants propagate vegetatively in nature by the forma-
tion of creeping underground stems (rootstocks or rhi-

Fic. 26. Rootstocks or rhizomes. Upper, four-year-old fleshy

rootstock of the Solomon’s-seal, which produces one stem each

year; lower, slender creeping rootstock of peppermint, which
produces several stems each year. After Gray

zomes); by creeping propagating roots; by stolons; by
tubers, corms, and bulbs; and by offsets. The rootstock
may be thick and fleshy—as it is in the Solomon’s seal
and the iris—or it may be slender—as it is in quack grass
and the hedge bindweed (Fig. 26). Slender rootstocks
send up shoots from the nodes. Plants with vigorous
slender rhizomes grow in colonies, forming dense sod or
masses; often—as illustrated by the zones of grasses,
sedges, and reeds around ponds, and in the saline marshes

[ 64 |

HOW PLANTS REPRODUCE

along our seacoasts—they grow so densely as to exclude
other plants.

Propagating roots resemble rootstocks but differ in
having no reduced leaves (scales) as do rootstocks, which
are true stems. Buds form on the propagating roots at
irregular intervals and grow up into shoots. Some trees,
such as the silver poplar, the wild plum, and the black
locust, form thickets of “suckers,” produced from propa-

Stolon

,
ca

os Stolon
Scale Leaf

Fic. 27. Runner or stolon of the strawberry. A plant is pro-
duced at each node. After Gray

gating roots. Some of our troublesome weeds, for ex-
ample, the Canada thistle and the field bindweed (Convo/-
vulus arvensis), produce propagating roots which are ex-
ceedingly difficult to eradicate. The common dandelion,
although it does not have creeping propagating roots, 1s
able to produce adventitious buds upon the thick tap
root, especially when this is injured. For this reason it ts
futile to attempt to destroy the dandelion by cutting
through the tap root below the crown, as is often done
to remove the weed from lawns. Buds form on the upper
end of the cut root and where there was one dandelion
before, two or three may take its place. Of course, re-

[65]

THE WORLD OF PLANTS

peated cutting at short intervals will exhaust the tap root,
but it is better to dig up the whole plant, root and all.
The runner is a creeping propagating stem, which grows
above ground and at intervals takes root and forms a new
plant (Fig. 27). The strawberry has such runners and the
varieties are propagated commercially by the new plants

Fic. 28. Tubers of the potato. A slender root-
stock swells at the end into a tuber. After Gray

formed. Bermuda grass produces rootstocks below ground
and runners or stolons above ground. The grass is often
propagated by planting pieces of the runner or root-
stocks at suitable intervals in prepared soil. Each piece
becomes a new plant and a field is thus soon covered. A
modification of the runner is seen in the black raspberry
in which a stem or cane bends over and takes root at the
tip. The walking fern does the same thing. The sugar-
cane is propagated commercially by cutting up the canes
into pieces and planting them; each piece must have a

[ 66 |

HOW PLANTS REPRODUCE

node on it because this has the bud from which a new
shoot springs.

The common white potato (the so-called Irish potato)
produces typical tubers (Fig. 28). The slender root-
stocks which first appear finally enlarge at the ends, thus
producing the edible potato. The “eyes” of the tuber are
buds from which the shoots grow. Below each bud or
eye (towards the base where the old rootstock is seen)
there is a little scale or rudimentary leaf. When the
potatoes are stored in bins, they are likely to “sprout”
toward spring, the shoots remaining white or tawny
(etiolated) if they are in darkness. In time the substance
of the tuber, mostly starch, is transferred to the shoots
and the tuber becomes shriveled. When the tubers are
used for propagation they are cut into pieces, as is well
known, but each piece (so-called seed) must have at least
one eye, otherwise no shoots could be produced. As soon
as the shoots reach the light they turn green through the
formation of chlorophyll. The potato (at least, many
varieties of it) may produce whitish or bluish flowers,
followed, less often, by berries or little balls containing
small seeds. The seeds will produce potato plants, but
not the particular variety from which they came; new
varieties are produced in this way, but to perpetuate the
variety the tuber must be used for propagation. Ifa tuber
is exposed to the sun it turns green (due to chlorophyll)
and begins to manufacture the same bitter substances
that are found in the normal stems and foliage.

In contrast to the tuber of the white potato we have the
fleshy root of the sweet potato, which, although it re-
sembles the white potato in that it stores nourishment and
becomes fleshy, is a true root with no eyes. When the
sweet potato is placed in soil under proper conditions it
produces new shoots; it is these shoots that are set out to
propagate the plant. The shoots come, however, from
adventitious buds.

Perennial herbs often produce at the base a series of

[ 67]

THE WORLD OF PLANTS

branches or shoots called offsets, or suckers. These may
be utilized in horticultural practice to propagate the
species. Some kinds of century plants and yuccas, the
banana, and the pineapple, are propagated in this manner.
Other perennials that form a crown of upright shoots are
propagated by dividing this crown, a method known as
division of the roots.

Bulbs—such as the onion, tulip, narcissus, and many
lilies—and corms—like the crocus and gladiolus—propa-
gate by daughter bulbs and corms (Fig. 29). A bulb is
made up of fleshy leaves, or scales, on a short supporting
stem, or button, at the base. The garden onion produces
also little bulbs at the top of the plant in the place of
flowers, and the tiger lily produces bulblets in the axils
of the leaves. These bulblets are used to propagate the
plant. A corm dif-
fers from a bulb
in being solid, the
stem having devel-
oped iat’ thesexe
pense of the leaves,
which are reduced
to scales upon the
surface.

The methods of

Fic. 29. Bulb of a lily. This is made Propagation men-
up of a series of overlapping fleshy tioned so far are
leaves borne upon a buttonlike stem, as those found in
shown in the section. After Gray nature or which
have been adapted
directly from nature. Man has invented a few other
methods, such as propagation by cuttings, by budding, and
by grafting.

Propagation by cuttings is a simple matter, theo-
retically. A twig or branch is cut off and placed in a root-
ing medium, such as soil, sand, or water. In time roots
are produced at the lower end and the buds develop to

[ 68 |

HOW PLANTS REPRODUCE

produce shoots. Some trees root so easily that a twig or
even a small log will send out roots. The willow and
poplar and many herbs grow readily from cuttings, and
among house plants the geranium is a familiar example of
those that can be thus reproduced, the cuttings being
often called “‘slips.” On the other hand, some plants are
grown with difficulty from cuttings, but in most of these
the difficulty arises from lack of knowledge as to the most
favorable time of year to take the cuttings, the best part
of the plant for the purpose, and the conditions most
favorable for the production of roots.

Budding is the process of removing a bud from one plant
and setting it into the bark of another (Fig. 30, right).
The peach is commonly propagated in this manner. A
bud is cut out so as to carry a narrow slice of the bark of
the twig and deep enough to include the cambium layer.
A slit just to the cambium is made in the young bark of
the plant to be budded, and under this the bud 1s slipped
and bound in place. The cambiums being in contact the
bud becomes a part of the twig. The twig above the bud
is cut off and the bud continues the growth in its place.
In practice a seedling of the peach is used for the stock
and to it when young the bud from the desired variety is
transferred. Hence the mature tree is of the variety
wished but the root system is that of the seedling.

The third process of artificial propagation is grafting
(Fig. 30, left). It differs from budding in that a whole
twig (the scion) of the variety to be propagated is united
with some hardy but otherwise undesirable plant (the
stock). A common method of grafting where the stock
and scion are the same size, is to cut each slantingly and
place them together. A little tongue is cut in each surface
to aid in keeping the scion in place. The junction is then
bound securely and sometimes covered with wax. The
cambiums unite and the scion becomes a part of the
stock. There are many kinds of grafts but in all of them
the cambium of the scion is placed in contact with that

[ 69 |

THE WORLD OF PLANTS

of the stock and the joint bound and protected until union
takes place. In root grafting the stock is a piece of the
root of a seedling. In top grafting the scion is grafted into
the top of a tree. Many varieties of fruit, ripening at
different times, may be made to grow on a single tree.

Fic. 30. Grafting and budding. Left, three

small scions being grafted on a large stock; center,

grafting of a scion on stock of the same size;

right, a bud ready for insertion in the stock.
After Strasburger

Furthermore, scions of one species may be grafted on
stocks of other species of the same genus or even of re-
lated genera. Almonds, peaches, apricots, and plums
may be grafted on one another; so also with quinces,
apples, pears, and hawthorns. The gardener often is able
to grow a desirable variety on the roots of a hardy species
under conditions which this variety would not withstand
on its own roots.

[70 |

HOW PLANTS REPRODUCE

Through grafting and budding man has been able
greatly to extend and to diversify his cultivation of use-
ful plants. These processes come down to us from pre-
historic times. One illustration will suffice to show how
useful the processes have been to man. At one time the
grape industry of France and of some other European
countries was threatened with extinction because of the
introduction from America of the root louse (PAylloxera).
The industry was saved by grafting the European grape
(the wine grape, Vitis vinifera) on the roots of native
American species that were immune to the attacks of the
insect.

[71]

CHAPTER IV

PLANT MOVEMENTS AND CARNIVOROUS
PLANTS

In the first chapter we stated that plants have no nervous
system. Nevertheless, they do possess to a limited degree
the power of motion. Very rapid movements are exhibited
by the motile spores of algae. These spores swim about
by means of fine hairs or cilia which vibrate so rapidly
that they can not be followed by the eye when viewed
through the microscope. These movements are autono-
mous; that is, they are due to some internal stimulus.

Movements in response to gravity and light, and the
movements of twining stems and tendrils have been men-
tioned; there are movements in the opening and closing
of flowers, and various movements in connection with
pollination and with dissemination; there are the “sleep”
movements that cause the leaflets of the oxalis and of the
pinnate leaves of many plants, especially of the Legumi-
nosae, to come together at night. Movements of leaflets
are caused by the unequal turgidity of little swellings
(pulvini) at the base. Under the influence of a stimulus
(light, heat, touch), the upper part of a pulvinus absorbs
water from neighboring tissue and becomes more turgid,
while the lower part of the pulvinus becomes less turgid.
This moves the organ downward. The reverse process
moves the organ upward. Such movements are usually
rather slow, but in a few plants they are so rapid as to
give the impression of nervous reaction.

The sensitive plant (Mimosa pudica), a native of the
Tropics that is often grown in northern greenhouses, is

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“des Ay-s,snua 4

CARNIVOROUS PLANTS

highly responsive to the touch (Fig. 31). The leaves are
twice pinnate—that is, the paired main divisions have

N
)

Fic. 31. Sensitive plant (Mimosa pudica). Left, leaves in
normal position; right, leaves after being touched or shocked.
After Kerner

paired subdivisions; the main petiole is an inch or. two
long and has a pulvinus at the base; on the main petiole

73)

THE WORLD OF PLANTS

there are four main divisions, each about as long as the
petiole and each with a pulvinus at the base; each division
has numerous small leaflets and each of these has a pulvinus
at the base. If the leaf is touched the main petiole re-
flexes quickly, the four divisions fall toward each other,
and the small leaflets close together upwards. In warm
sunlight these movements are almost instantaneous. If
one pinches the end leaflet of a division without dis-
turbing the rest of the leaf, the stimulus travels down the
division, closing one pair of leaflets after another, then
the four divisions come together, and finally the main
petiole droops. If one hits a single leaf carefully without
shaking the stem, this leaf will reflex and in a few moments
the leaf above and the one below will do the same, and so
on until the stimulus dies out. The leaves return slowly
to their normal position in a few moments. It 1s evident
that there exists a channel by which the stimulus is carried
through the leaf and through the stem. There appears
to be here a rudimentary nervous system.

The Venus’s-flytrap is another plant that responds to a
stimulus in an almost instantaneous manner (Plate 12).
This plant grows in bogs in eastern North Carolina. The
leaves have at their ends a nearly circular, flat “trap”
about an inch in diameter, through the middle of which
runs the midrib of the leaf. The edge of the trap has a
number of long, sharp teeth and in the central part of each
half are three little spines shorter than the marginal teeth.
When an insect strikes one of these spines the trap snaps
shut quickly enough to catch the intruder. The trap at
once exudes a juice over the insect and the soluble parts
are digested and absorbed by the plant. It is curious
that if the spines are touched, say, by the end of a pencil,
the trap closes but soon opens again, whereas if an insect
is caught the trap remains closed several days until the
nitrogenous food is digested.

Other plants besides the Venus’s-flytrap have special
structures by which they can catch small insects. Such

[74]

CARNIVOROUS PLANTS

plants have been called carnivorous, because they not only
catch insects but digest them with the aid of a special
secretion and absorb the nourishment. On the other
hand some plants secrete sticky fluids on their stems or
leaves, which may catch insects, but the plants do not
digest and absorb their victims. For example, the catch-
fly secretes, at the time of flowering, a sticky substance
in a zone on the internodes, the purpose of which appears
to be to prevent ants from climbing the stems to the
flowers, where they would steal nectar intended for insects
that aid in pollination. Incidentally in this connection,
we find that plants are protected from animals in various
ways. Thorns, spines, and prickles all serve a protective
purpose, as seemingly do the stinging hairs of nettles and
some other plants. Unpalatable substances in the foliage
protect against grazing animals, and a few plants have an
active substance that poisons when the foliage is touched.
The common poison ivy and poison oak belong to this class.
The deadly upas tree of the East Indies yields an active
poison from its milky juice, but the stories that it destroys
all life within a radius of fifteen or more meters are pure
invention. Equally without foundation are the hair-
raising tales of a plant (from some little-known tropical
country, of course) that has long tentacles by which it
grasps stray victims and sucks their blood.

The best known carnivorous plants, aside from the
Venus’s-flytrap, are the bladderwort (Utricularia), the
sundew (Drosera), and the pitcherplants (Sarracenia and
Nepenthes). The bladderwort floats in the still waters of
ponds by means of numerous small bladders each about
the size of the head of a pin. Each bladder has a small
entrance guarded by a trap door, through which minute
water animals can enter but can not escape. The animal-
cules soon perish and the organic substances of their
bodies are absorbed.

Numerous stalked glands on the surface of the leaves
of the sundew exude a sticky substance by which insects

[75]

THE WORLD OF PLANTS

are caught. The glands glisten in the sunlight and suggest
the plant’s name—sundew. If an insect touches the sticky
surface it remains stuck unless it is powerful enough to
free itself. Small flies can not get away. Very soon the
stalked glands, or tentacles, close down on the victim and,
if it is not already there, gradually move it towards the
center where it will be covered with the greatest number of
glands. It is to be noted that not only the tentacles in
contact with the insect turn down, but finally all the
tentacles (of species like D. rotundifolia) bend over to
come in contact with it. A digestive fluid is then secreted
and the substance of the victim is absorbed. It is signifi-
cant that rain and wind will not cause the tentacles to
act, and inert bodies like grains of sand, or even non-
nitrogenous organic substances such as sugar, cause only
a slight disturbance; but a living insect or a piece of meat
sets up the characteristic action.

Pitcher plants are so called because the leaves have the
form of a cup or pitcher and are more or less upright. The
structure is such that insects can easily crawl into the
pitcher but are prevented from escaping by stiff hairs
directed downward around the mouth of the pitcher, and
by the slick inner surface. It appears that the leaves
extract nourishment from the macerated and decaying
animals.

As all the carnivorous plants live in bogs or moist soil
in which there is a deficiency of nitrogen, it is thought that
this peculiar carnivorous habit may be beneficial in sup-
plying the needed element.

CHAPTER V
Be oOC LE TIES

THE earth, except in regions of perpetual snow or extreme
desert, is now covered with plants. The conditions under
which these plants grow, of course, differ widely in differ-
ent quarters of the globe; plants found in the Tropics
could not exist in Arctic regions; plants of the seashore
would fail upon mountain tops; swamp plants would suc-
cumb to desert conditions. It is evident to the most
casual observer that under a certain set of conditions—
those found in a marsh, for example—there grow a certain
group of plants that do not grow elsewhere. The seeds of
plants are scattered far and wide and are produced in
quantities far exceeding what could possibly find space to
grow. There is always strenuous competition, first for a
place to germinate, and then for soil, air, water, and light
to bring seedlings to maturity. The Great Teacher was
familiar with this law, as is shown by the parable of the
sower (Luke 8:5-8). Much of the seed sowed by the
sower failed to survive, but a part, falling on good ground,
“bare fruit an hundredfold.”’ There is in nature a con-
stant “struggle for existence” which, broadly speaking,
results in the “survival of the fittest.” Each species must
compete with all other species adapted to a particular set
of conditions; the individual must compete with other
individuals of the same species—the severest competi-
tion of all.

Furthermore, plants in possession resist displacement.
In fact, the spread of species often depends upon the
opening of soil by some catastrophe. Virgin forest may

[77]

THE WORLD OF PLANTS

remain indefinitely, excluding all aliens even of the same
species, until a hurricane sweeps through or a giant tree
overturns, making a place for seed. Prairie sod may con-
tinue unbroken except here and there by gophers and
prairie dogs, by the tramping and pawing of buffalo or
cattle, or by some other casual circumstance, for hundreds
or even thousands of years.

Each type of environment found on the earth—whether
it- be rocks or forest, seashore, plain, or marsh—supports
the plants suited to it. Some plants found in a certain
situation could grow under other conditions, though they
might not be able to compete with other species. Thus
the bald cypress is found growing naturally in swamps—

“cypress swamps’’—but it thrives also when cultivated
in ordinary soil in parks. Man’s crop plants are soon
exterminated by the encroachment of native species if he
does not protect them.

The study of the adaptation of plants to their surround-
ings is known as ecology. In a broad way, plants may be
classified on the basis of environment into four groups:
Hydrophytes, xerophytes, halophytes, and mesophytes.
The first group (hydrophytes), adapted to an excess of
water, are found in water or in wet places; they may be
submerged, or their leaves may float; or they may be
emersed but have their roots in a saturated soil. It might
be supposed that hydrophytes would have no difficulty
in getting water; nevertheless they are often provided
with leaf structures like those found in some desert plants
to enable them to resist evaporation. For example, the
sweet flag and the cat tail have thickish vertical leaves ex-
posing a comparatively small surface. It so happens that
in the early part of the season the leaves of these plants
are subjected to evaporation at a time when the roots are
surrounded by water so cold that it can not be readily
absorbed. Consequently, in spite of the abundance of water,
the leaves—were they not protected by a special structure—
might wilt because of the inactivity of the roots.

[78 ]

PEANT SOCIETIES

The second group (xerophytes) grow on soil in which
there is too little water; for example, sandy soil, which
will not hold water; the soil of arid regions, which suffers
from a deficiency in rainfall; or rocks, which shed water
rapidly. The group includes most epiphytes—plants that
grow upon the surface of other plants, especially trees,
but are not parasitic upon them (Plate 13). The prob-
lems for xerophytes are to prevent too great a loss of water
through evaporation, and to store water during a favor-
able season to last them through a period of drought.
They meet these problems by a variety of structures and
adaptations such as a thick epidermis to the leaf-blades,
waxy, sticky, or hairy leaf surfaces, mucilaginous juice,
great reduction of leaf surface—as in the cactus—rolling
of the blades so that the breathing pores (stomata) are
on the inner surface, and fleshy underground stems, bulbs,
and fleshy roots that store water beneath the surface of
the soil. All these contrivances are adaptations to a
small water supply.

The third group (halophytes) are adapted to soil with
an excess of mineral salts. (The excess mineral matter in
soils supporting halophytes is usually salt or soda, but
there may be an excess of other mineral constituents.)
Halophytes are found along the seacoast, in the coastal
marshes, and around salt lakes or springs. Undrained
basins accumulate mineral constituents at the surface of
the soil by evaporation. The problem for halophytes is to
obtain sufficient water without committing suicide by
taking in an excess of mineral matter. Consequently
such plants have many of the structures found in xero-
phytes to reduce evaporation. The leaf surface is re-
duced, the plant is fleshy, the juice is mucilaginous, or the
leaf-blades are hard and fibrous. Bulbs and fleshy root-
stocks or roots are not common as there is usually no need
for storage against drought or aridity.

The fourth group (mesophytes) include plants having a
sufficient but not excessive supply of water; they grow

[79]

THE WORLD OF PLANTS

under medium conditions. Typical mesophytes such as
are found in tropical rain-forests have broad, thin leaf-
blades through which the water in the plants readily
evaporates; and they lack special structures to resist
evaporation or to store water. However, many plants
that are classed as mesophytes are subjected to xero-
phytic conditions during a part of the year and possess
adaptations to meet them. For example, the deciduous
trees of the temperate zone drop their leaves for the winter
season, when it is difficult for the plant to obtain water,
and evergreen trees meet winter conditions by a reduction
of foliage and by having resinous sap.

Of course, the lines are not sharply drawn between the
four groups mentioned but the classification serves as a
basis for study.

During the long period that plants have existed upon
the earth physical conditions have gradually changed and
plants have had to adapt themselves to the changes or—
as fossil records show—they have been exterminated.

THe GEOGRAPHICAL DISTRIBUTION OF PLANTS

Plants, as we have said, cover the earth except in
regions of perpetual snow or extreme desert. Lack of
water precludes vegetable growth, but such lack is rarely
or never permanent for any region of the earth; the most
arid regions receive rain occasionally though it may be
—as on the coast of northern Chile—after periods of
drought lasting several years. After these rare rains
vegetation springs forth with astonishing quickness and in
unexpected abundance; the vegetation may last possibly
only a few weeks, but within this time it matures seed
which lies dormant until the next rain. Thus it is that
land plants are found from sea level to the edge of per-
petual snow on the highest mountains, and from the
equator to perpetual snow around the poles. Even the
sea supports abundant vegetation along much of its mar-
gin as far below the surface as light will penetrate; and

[ 80]

PLANT SOCIETIES

even far out from land it supports near the surface a
floating population of microscopic plants (diatoms)
unbelievable numbers, these plants forming in the last
analysis the basis of sustenance for most of the animals
of the sea.

The theory of evolution, to which all modern botanists
subscribe, holds that all species of plants of the present
are derived from other but related species of plants of the
past, and that all plants are genetically connected,
though the lines of descent may have begun to diverge
millions of years ago. If this is so, why do we find such
an intricate mixture of kinds of plants in any area of
vegetation that we may select? Why do we find in any
given locality plants growing together, cheek by jowl,
that may represent all the chief divisions of plant life?
Our answer might be that in the evolutionary develop-
ment of species the lines of descent from remote ancestors
have, through repeated divergence, become entangled.
The case is not so simple. We find closely related plants
growing in regions remote from one another; we find a close
relationship between the plants of Japan and those of
the northeastern part of the United States; we find indi-
viduals of the same species on widely separated mountain
tops with no representation between; certain groups of
plants may be represented in South Africa and South
America. How are these gaps to be explained?

The distribution of plants within a single area of uni-
form conditions may be explained by the methods of seed
dispersal already discussed (see page 55). The wind will
blow fluffy or winged seeds to a considerable distance;
animals may carry burs from one point to another; water
courses may carry seeds down stream. These factors will
account for much of the local intermingling of species and
indeed will result in a slow migration of species. But to
explain the present geographical distribution of plants
over the earth’s surface, we must look for causes oper-
ating over wide areas and over long periods of time.

[81]

THE WORLD OF PLANTS

Some of these causes may be effecting changes at the
present time; some have effected fundamental changes in
past geological epochs.

One of the causes operating at the present time is the
introduction, mostly unintentional, of the plants of one
country into another through the agency of man. The
extensive interchange of products between remote coun-
tries makes the accidental transportation of seeds com-
paratively easy. Alfalfa seed grown in Europe and 1m-
ported for use in Kansas may bring with it seeds of
European weeds. Wool from Argentina may carry seed
to Germany, and some of it may acquire a foothold. A
summary of the flowering plants in Gray’s Manual of
Botany of the Northeastern United States shows that of
about 4,000 species, 666 are introduced. Certain species of
introduced grasses (bromes, wild oats, barley grasses)
have driven out native species from large areas in the
valleys and foothills of California. Introduced species
have so thoroughly displaced the original flora in the
vicinity of Honolulu that it is difficult now to find a
native species—except for certain strand plants—within
many miles of the city. A visitor unfamiliar with the
history of the Hawaiian flora would think that the guava,
the lantana, and Hilo grass (Paspalum conjugatum) were
native plants, so widespread and abundant are they.
Modern methods of transportation have accentuated this
mixing of floras, but for thousands of years plants have
been carried along the ancient trade routes.

Botanists have noted the wide distribution of the
typical plants of fresh-water ponds and marshes. This
is chiefly due, no doubt, to the dispersal of the seeds of
these plants by migrating water fowl; the seeds are car-
ried in mud upon the feet of the birds or to a less extent
upon the feathers. This method of dispersal is especially
efficacious because the seeds are deposited in places
suited to their germination and subsequent growth.

Plants tend to migrate slowly from one region to an-

[ 82 ]

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tl ALVId

PUANT SOCIETIES

other over the land surface where there are no barriers
such as high mountain ranges or arid wastes. This
gradual spreading has been going on for untold ages. But
it is apt to meet with obstacles, causing great changes in
the composition of floras, for we know that the topography
of the earth has undergone many alterations in times past;
land areas have risen or fallen in relation to sea level;
certain lands now separated by wide stretches of water
are known to have been connected in former epochs,
when migration, which is impossible now, could have
progressed freely. We have material evidence in the fossil
remains of plants preserved in the rocks that great
changes have taken place in the composition of floras.
It is easy to see how they must have come about. The
alterations in topography effected changes in the climate,
just as a diversion of the Gulf Stream through a channel
in the region of Panama would profoundly affect the
climate of the British Isles; such a change of climate
would, of course, alter the flora.

Preceding the last Glacial epoch when the ice cap ex-
tended far down into temperate regions—for example, as
far south as Iowa and northeastern Kansas in America—
a mild climate prevailed in Arctic regions, as shown by
fossil remains of palms and other plants typical of warm
regions. As the Glacial epoch developed, these plants
were gradually driven southward. Had the conditions
along the parallels of latitude been uniform, the plants
would have followed the meridians of longitude. The
conditions, however, were very diverse. In the south-
ward movement species were extinguished except as they
encountered favorable conditions. Thus it came about
that certain species that had enjoyed a continuous area
of distribution in high altitudes before the Glacial epoch
divided as they were driven southward, part following
the east Asiatic coastal region and another part following
the east American coastal region. Only in these regions
did these species find suitable conditions; elsewhere they

[ 83 ]

THE WORLD OF’ PLANTS

were exterminated. The migration was so slow that the
part pushed into eastern Asia had time to differentiate
somewhat from the part pushed into eastern America.
Nevertheless, at present the flora of Japan and north-
eastern Asia is evidently closely related to that of north-
eastern America—much more closely related than it is to
the flora of the Pacific Coast of America. There are many
genera of plants in which some of the species are found in
northeastern America and some in northeastern Asia but
none in any other part of the world.

Another result of the southward push of the great ice
cap is the small number of species in the present flora of
Greenland as compared with the flora of that part of
North America in the same latitude. On the continent the
ice cap drove the plants southward over the land, so that
on the retreat of the ice they gradually followed north-
ward; but in Greenland the plants had, as it were, been
driven into the sea so that there were none to follow the
ice back. The present flora is in the main the result of
accidental introductions since the Glacial epoch.

Still a third result of the descent of the ice sheet is the
occurrence of many Arctic species on the tops of high
mountains in temperate regions. Species driven to these
peaks by the ice were unable to follow the retreating
glaciers back, because in descending the mountains they
came into contact with a temperate flora, which they could
not dislodge. A certain grass (Trisetum spicatum), com-
mon at low altitudes in Arctic regions and circumpolar in
its distribution, extends southward along the mountain
ranges that run north and south. It is found on the sum-
mits of the White Mountains, of the Adirondacks, and of
Roan Mountain (North Carolina), in the alpine regions
of the Rocky Mountains, of the Sierra Nevada, and of
the high mountains of Mexico and the Andes, and de-
scends to low altitudes again in the Antarctic regions. It
is also found in the Himalayas and other high mountains

[ 84]

PLANT SOCIETIES

of the eastern hemisphere, including those of New Zealand
and Australia.

One other factor in the world-wide distribution of plants
is transportation by ocean currents. Much information
on ocean currents has been obtained by consigning bottles
to the waves at various places, with instructions for their
return when picked up. Many such bottles have been
recovered at long distances from the point whence they
started. Botanists (notably H. B. Guppy) have investi-
gated the transportation of seeds and fruits by these cur-
rents. Plants can profit by the ocean currents only when
their seeds (or fruits) are able to float for a long time, are
not injured by the seawater, and find favorable conditions
for germination and growth in the places where they are
deposited. Seeds of West Indian plants have been found
on the coasts of Norway, of England, and even of coun-
tries as far south as Morocco and the Cape Verde Islands;
they were transported to all these places by the Gulf
Stream.

It is probable that ocean currents constitute the chief
factor in the distribution of strand plants. The south
equatorial current readily brings seeds from the coast of
Africa to Brazil, thus partly accounting for the similarity
of the strand plants of the two regions. The flow of ocean
currents in past ages may account for what seems at pres-
ent to be an anomalous distribution of certain strand
plants. For it must be recalled that, because of different
configurations of the land surfaces, the ocean currents in
past geological ages flowed differently from what they
do at present.

When it is remembered that the factors controlling the
distribution of plants have for the most part acted for
millions of years and under conditions known to us only
in part, that through all these ages the evolution of plants
has been going on, and that an indefinite number of con-
necting links have disappeared, the present complexity
of distribution is not so surprising.

[85 ]

CHAPTER VI
HOW PLANTS ARE RELATED

Tue plants inhabiting the earth today are the surviving
descendants of countless generations. To determine how
they are related to each other is one of the fundamental
problems of botany. The classification of plants is an
attempt to show this natural relationship—an attempt
based on the study of the relatively very small part of the
vegetable kingdom living today, and of the still smaller
part represented by fossils. The present flora of the
world is a cross-section of the lines of descent that extend
far back for untold generations. Some of the extinct
links are revealed to us in the fossil remains in the rocks,
but most of them are lost. We are forced: to base our
classification on similarities.

Herbert Spencer stated in his somewhat stilted lan-
guage that “organisms are classified according to the
totality of their morphological resemblances.” The rela-
tionship between some plants is evident, so evident that
observant mankind has recognized certain groups since
time immemorial. The palms, the pines, the oaks, the
legumes, the crucifers, and the composites, the grasses,
the ferns, and the mosses have always been recognized
as groups each containing related kinds of plants. But
there are many plants whose relationships are not at all
clear. These are placed provisionally at certain points in
our classification but with the understanding that on fur-
ther study they may be placed elsewhere.

Plants in general fallnaturally into four great groups: the
thallus plants, the mosses, the ferns, and the seed plants.

[ 86 ]

HOW PLANTS ARE RELATED

TuHatius Piants (Thallophyta)

The thallus plants, the lowest group, consist of kinds
which are not divided into stem and leaf. In the simplest
forms the plant body is made up of single cells, or of sim-
ple or branched filaments; in the higher forms the plant
body may become rather complex but still not be dif.
ferentiated into a stem and leaves.

There are two main groups—algae and fungi—based
on the presence or absence of chlorophyll. The algae pos-
sess chlorophyll, though it may be masked by a red or
brown coloring matter. The fungi are devoid of

chlorophyll.
Algae

The algae (see Part III, page 165) are confined almost
entirely to water or wet places. The forms that live in
the ocean, usually called seaweeds, may be green, brown,
or red, whereas most of the fresh-water algae are green
or bluish-green. The green coating sometimes found on
the north sides of brick buildings and of tree trunks, near
the ground, is made up of microscopic one-celled or sim-
ple forms of green algae. The fresh-water and marine
plants called diatoms are one-celled, yellowish algae,
which are peculiar in having a siliceous cell wall; under
the microscope this wall is seen to be beautifully figured
and ornamented. Because of the silica in the cell wall,
diatoms retain their shape after the death of the cell
contents. These minute plants exist in enormous num-
bers in the sea, where they float unattached and are shifted
about by the currents. Directly or indirectly they are
the basic support of most of the animal life of the sea.
Diatoms are also widely distributed in fresh water and
compose the slimy coating commonly found on sticks and
logs in streams, ponds, and ditches. In past ages these
minute algae have existed in such numbers that their
siliceous remains have formed great beds of diatomaceous
earth on the sea bottom. In the course of ages geologic

[87]

THE WORLD OF PLANTS

changes have lifted many of these beds above sea level
and made them accessible to commercial exploitation.
For example, the material is mixed with nitroglycerin and
used in making certain grades of dynamite. Some beds
are several hundred feet in thickness and an idea of the
enormous numbers of diatoms composing them may be
obtained when it is realized that one cubic centimeter may
contain more than two and a half million diatom shells.

Some of the filamentous algae form the green scum
(pond scum) often seen on stagnant water in bright
weather. The bubbles of oxygen formed during photo-
synthesis are quite evident and tend to float the felty
mass. At night the filaments sink below the surface.
Duckweeds also form a scum on the surface of stagnant
water (see page 113), but these plants have a small flat
plant body and are not made up of filaments or felty
masses.

The seaweeds are found chiefly along rocky seashores
between tide limits, though sometimes they may occur
as much as six hundred feet below the surface. They
have rootlike processes by which they hold fast to an
anchorage, but these holdfasts do not absorb nourish-
ment and do not have the structure of roots. The large
brown seaweeds are usually called kelps. The giant kelp
of the Pacific Coast may attain a length of 500 feet. Cer-
tain kelps that look like rubber tubing with large bladder-
like swellings are commonly washed up on our western
shores. Seaweeds exposed to the air during low tide are
protected from drying out by being tough and mucilagi-
nous. A mass of the seaweed sargassum (Fig. 32) floats
in an immense eddy of the Atlantic Ocean northeast of
the West Indies; it covers an area of probably two hundred
thousand square miles, which is known as the Sargasso
Sea. The floating seaweed propagates vegetatively. The
little berrylike bodies on the alga are not fruits of the
plant but bladders by which it floats. The plant body

consists of a central axis with expanded branches which

[ 88 |

PLATE, 15

. Wheat showing stems and leaves infected with the black rust.
Courtesy of the U. S. Bureau of Plant Industry

PLATE 16

Plump healthy kernels of wheat (upper) and kernels shriveled by
wheat rust (lower.) | Courtesy of the U. S. Bureau of Plant Industry

HOW PLANTS*ARE RELATED

superficially simulate the stems and leaves of higher
plants. Sargassum in small masses is frequently seen
from the decks of transatlantic steamers.

Certain seaweeds
are edible — among
them the species from
which is obtained
agar, or agar-agar, a
substance much used
in laboratories for
growing bacteria in
artificial cultures.

Fungi

Possessing no
chlorophyll, the fungi
must obtain their
sustenance from living
or dead organic mat-
ter. If they derive
their nourishment
from living plants or
animals they are
parasites; if from dead Fic. 32. Sargassum. The globular

material, they are objects are bladderlike floating or-
saprophytes. The gans. After Kerner

simplest forms of

fungi, the bacteria, are of interest to us because they
cause fermentation, putrefaction, nitrogen fixation in the
soil (see page 27), and especially because they cause many
of the serious diseases of the human race, and of domestic
animals and cultivated plants. Among human diseases
caused by bacteria are cholera, diphtheria, lockjaw,
pneumonia, tuberculosis, and typhoid fever; among the
diseases of domestic animals, anthrax, black-leg, and
chicken cholera; and among the diseases of plants, the
soft rots of vegetables and the blights of cucumber and

[89]

THE WORLD OF PLANTS

potato. The quick action of bacteria in producing fer-
mentations, diseases, and so on, is due to their rapid
multiplication, some kinds dividing as often as once every
twenty minutes. Incidentally, some contagious diseases
are caused by protozoans, a simply constructed group of
the animal kingdom.

Until within the lifetime of many now living, putrefac-
tion was thought to be due to “spontaneous generation.’
If a decoction of hay or of meat was exposed to the air for
a short time, it decomposed and bacteria appeared. As
nothing had been added to or had been seen to enter the
liquid, the natural supposition was that the organisms
found in the decomposing material must have originated
spontaneously. Then in 1864, Pasteur, the great French
scientist, showed conclusively that putrefaction could not
take place if certain precautions were taken to exclude
germs floating in the air. He placed boiled decoctions in
two test tubes, leaving one open and protecting the other
by a plug of cotton which would not exclude the air. The
first decomposed; the second did not, because the minute
germs in the air had been filtered out. He had great
difficulty in overcoming the prejudice of ages, but the
younger men were won over to his views. The life of
Pasteur reads like a novel. He was the first to show that
rabies was carried by a germ and he invented a cure, con-
sisting of antitoxic serum, for this dreaded disease. Again
he had to fight the prejudices of his colleagues. How he
saved the life of a child that had been bitten by a mad
dog is certainly one of the romances of science.

The active part of baker’s yeast is a microscopic plant
similar to bacteria. The single-celled individuals propa-
gate by budding instead of by division. One side of the
cell bulges out to form a “‘bud” which soon becomes as large
as the original or mother cell. The new cells may remain
attached as a colony or may separate. During metabolism,
the yeast plant gives off carbon dioxide. It is this gas
which makes the bubbles in dough and causes it to “‘rise.

[go]

HOW PLANTS ARE RELATED

The higher fungi are responsible for many of the mala-
dies of plants, and constitute a serious drain on our agri-
culture. One author estimates that the reduction in the
yield of cereals in the United States due to smuts (Plates
15 and 16) alone amounted during one recent year to

Gi
=e

Fic. 33. Left, lichen of the leafy sort growing on rocks (the
cups contain the spores); right, cross section of a leafy lichen (the
filaments belong to the fungus). After Kerner

160,735,000 bushels. Other fungi also take their toll.
The more common fungous diseases are smuts, rusts, and
parasitic mildews such as the potato mildew and the grape
mildew. The filaments of the fungus penetrate the cells
of the host plant or spread over the surface and send down
little sucking processes into the cells. The spores are the
more conspicuous part and are usually formed on the
surface where they can be scattered by the wind. Wheat
rust and corn smut are familiar examples.

Another series of fungi—often referred to loosely as
fleshy fungi—include mushrooms, toadstools, puffballs,
bracket fungi, and their allies. The conspicuous part of

[91]

THE WORLD OF PLANTS

the fungus is the spore-bearing body, whereas the myce-
lium, or threads, of the plant body penetrate the support
on which they grow. If the cap of a toadstool is cut off
and laid, under side down, on black paper for a few hours,
the spores will drop from the gills and form a print of the

Fic. 34. A moss. The capsules at
the summit contain the spores.
After Schimper

gills upon the paper.
Most of these fleshy
fungi are saprophytic.
The common mush-
room, cultivated for
food in dark cellars,
illustrates the manner
in which saprophytes
live. Upon. ‘a’ “pre-
pared bed of decom-
posed organic matter
is planted the spawn,
or mycelium, of the
mushroom, a_ felty
mass of white threads.
After a time the spore
bodies of the fungus
make their appear-
ance and are gathered
for sale.

To be considered
along with the fung1
is a group of very
remarkable __ plants,
the lichens. A lichen
consists of a combi-
nation of a species of
fungus with a species

of alga (Fig. 33). The combination (for life) is called
symbiosis because it is mutually beneficial. The fungus
surrounds and protects the alga and supplies it with water
and mineral salts; at the same time it feeds upon the alga,

[92]

—————————

HOW PLANTS ARE RELATED

absorbing its excess nutriment. Although parasitic on
the alga, the latter is not destroyed by the fungus but
remains in good condition. The relation is somewhat
like that between man and dairy cattle.

Lichens are common, They form the grayish-green
leafy coatings on the bark of trees, the red, yellow, and
black stains on rocks, and the flat or curly thallus on the
ground. The so-called reindeer moss of northern regions
which furnishes so much food to caribou and reindeer is a
lichen, and so is the Iceland moss once widely used in
pulmonary diseases.

Mosses (Bryophyta)

The second great group of plants, the mosses (Fig. 34),
are familiar to all who roam the woods. They have a
stem and leaves but no distinct vascular system. They
absorb moisture through the roots when these are well
developed, and also directly through the leaves when
these come in contact with dew or other moisture. The
spore bodies are in the little capsules at the summits of
the stems.

In general the mosses are of little use to man. The
sphagnum moss, which forms great bogs (peat bogs) in
northern regions, 1s used for packing and in the nursery
trade for potting plants. Also, the disintegrated vegeta-
tion of old bogs, consisting largely of sphagnum, gives us
peat, which in some countries is an important fuel.

Ferns (Pteridophyta)

The ordinary ferns (the third plant group), are common
undergrowth plants of the forest, being especially num-
erous in the wet forests of the Tropics, and some kinds
are found on rocks and on trees (Fig. 35). In warm
regions ferns may become trees, resembling palms and
possessing distinct trunks and great crowns of spreading
fronds. The fern group differs from the preceding two
large groups in having a distinct vascular system. The

[93 |

THE WORLD OF PLANTS

spores are borne for the most part in lines or dots on the
under sides of the leaves or fronds (Plate 17).

Allied to the true ferns are the club mosses—which in-
clude the ground pine,
and the selaginella, the
mosslike decorative
plant of our green-
houses—and the horse-
tails; or scouring
rushes, with _ stiff,
jointed, leafless, green
stems, which are harsh
because of the silica
contained in the tissue.
The ferns have also
some other less com-

a PW Senne retrsA
By ASSESS ee As
Sater

ao} mon allies. The fossil
ect ate evidence shows that
SSS SQV . .

ons in past ages, especially

in the Carboniferous

Fre.i95.) A fern. |) The leaves or 7
fronds have a peculiar coiled form oe a a Ereee
when young. After Strasburger ominate the vege-
tation of the earth.

SEED PLants (Spermatophyia)
This, the fourth and highest group of plants, includes

most of the ordinary conspicuous plants with which we
are familiar. It is distinguished from the three preceding
groups in that its members form seeds with an embryo.
There are two distinct subdivisions of the seed plants—
the gymnosperms and the angiosperms.

Gymnospermae

The gymnosperms (meaning naked seeds) are also
loosely called conifers because many of them bear cones
in which are the seeds; and in northern regions they are
often called evergreens because most of them remain

[94]

PEATE, a7

Under side of a fern leaf, showing spores; much enlarged. In this
species the spore cases are partly hidden by a thin membrane

PLATE 18

Px epee
AW y \ NC) Z
- Na of War ly +

ve er, lee
ane

WseQV gs
ae! a

de)

a. W
a
a

“0S iS
ee
oe
| sg Ae a
. Ze
et pe . SS
ty oe.
ss
‘ae ¢,
26
@
hd

} ‘ 7 : 4 >"
eaten ee, eical
Batt sys te. 5am? ¢
4 oi i Os ee

o-*
Joes

oe
%,
s

\) +

a)
es Vo

tS
a,

ler a microscope, show-

Part of cross section of a palm stem as seen unc

ing the vascular bunc

Courtesy of the

les distributed through the pith.

S. Forest Products Laboratory

HOW PLANTS ARE RELATED

green through the winter, whereas other trees are decidu-
ous. This difference does not hold good farther south,
where many other kinds of trees are evergreen. To the
gymnosperms belong the pines, spruces, firs, larches, the
yew, junipers, sequoias (redwood and big tree), and many
others, including the cycads which resemble palms and
have a stout, short trunk and a tuft of large leaves with
numerous slender leaflets. The cycads are thought to be
the most primitive of the gymnosperms and were abun-
dant in earlier geologic ages.

The flowers of the gymnosperms differ from those of
the angiosperms in that the ovule is not inclosed in an
ovary, but lies naked, though usually protected by sur-
rounding scales. The pollen does not have to grow
through the tissues of a style and ovary to reach the ovule
but can penetrate the ovule directly. The leaves of most
kinds are needlelike, as in the pines, or scalelike, as in the
red cedar (a kind of juniper).

Angiospermae

The angiosperms (meaning inclosed seeds) are the ordi-
nary flowering plants, the ovules of which are borne within
a closed ovary. This group is split into two large subdi-
visions according to the number of cotyledons of the em-
bryo: the monocotyledons and the dicotyledons.

The structure of the embryo of the maize, already de-
scribed (see page 59), is characteristic of the monocoty-
ledons in so far as the single cotyledon is concerned. The
parts of the flower (sepals, petals, stamens, and stigmas) in
the monocotyledons are usually in threes or sixes, and the
usually parallel-veined leaves are entire (that 1s, the edges
are not notched or lobed). The structure of the stem
differs from that of the dicotyledons. The bundles of
conducting tissue are not distributed in a definite ring
with a central pith but are arranged irregularly through
the pith (Plate 18). The maize (corn) stem shows this
distribution characteristically, but the wheat and other

[95 ]

THE WORLD OF PLANTS

hollow-stemmed grasses appear to depart from it because
the central part shrivels at an early period of growth and
the bundles are forced into an annular zone; however,
within this zone they are irregularly distributed, as may be
observed with a good lens. Furthermore, the stems (with
rare exceptions) have no cambium and therefore can not in-
crease in diameter after the tissues of the stem have reached
the mature form. Thus the palms, at the base of their
cluster of leaves, slowly form a trunk which, when it emerges
above ground, is as large as it ever will be at that point.

The embryo of dicotyledons has two cotyledons, as de-
scribed on page 60. To this group belong all our northern
forest trees except the conifers, and, so far as the number
of species is concerned, probably two-thirds of the herba-
ceous plants. The flower parts are usually in fours or
fives and the leaves are usually net-veined. The vascular
bundles are distributed in a ring around a central pith.
Since there is an actual or potential cambium in the bun-
dles, the stems of dicotyledons can grow in diameter as
described on page 14.

In their system of classification Engler and Prantl num-
ber 280 families of flowering plants. The list appears on
paper in lineal sequence; the evolution of plants, however,
has not developed along a single line but in many direc-
tions. The dicotyledons follow the monocotyledons, but
the highest group of the latter—the orchids—are much
more complex than the lower groups of the dicotyledons.
Relationships are revealed also in the structure of the
plant body itself, but the flowers are less subject than is
the plant body to modification as a result of environment,
and so are the best key to genetic relationships.

The relationships of the better-known flowering, plants,
particularly those of the temperate zone, are given in more
detail than we have room for here in an Appendix at the
end of this Part (see page 112). The amateur gardener
may discover in it some rather unexpected affinities be-
tween the plants with which he is empirically familiar.

L 96 |

CHAPTER VII
HOW PLANTS ARE USED BY MAN

Mankinp is absolutely dependent for his existence upon
plants. He utilizes animals, but they in turn are depen-
dent upon plants. In the story of creation plants ap-
peared on the third day, whereas animals were not
created until the fifth day, and man himself not until the
sixth. So early was it recognized that man and other
animals could not live without plants.

Man has used plants since he appeared on earth, of
course, but at first he took them as he found them, eating
such roots and fruits as were edible. Very early in his
career, however, he began to adapt plants to his use in
ways that other animals have never learned, an achieve-
ment that distinguishes him from these animals and to
which in the last analysis he owes his dominant place in
the animal kingdom. Long before the dawn of history
man had learned to gather and store seeds, and to culti-
vate many plants, thus securing a larger supply of more-
palatable food. He somehow learned to burn wood, a
tremendous advance in his career. He clothed his hairless
body with skins of animals mostly, but very early he
devised ways to make cloth out of bark and to weave the
fiber beaten out of certain stems.

The most primitive races today utilize plants in many
ways that require intelligent preparation. In fact, savage
races show a surprising knowledge of their native plants
and of the uses to which they may be put.

It is an interesting fact that nearly all the important
and widely cultivated economic plants of today have been

197]

THE WORLD OF PLANTS

in cultivation since prehistoric times. Aside from forage
plants and ornamentals, very few important economic
plants have been brought into cultivation within historic
times.

Foops

The staple foods, with the exception of the legumes—
in which there is a considerable proportion of protein
(nitrogen-containing material)—are largely starch; these
are parts of plants in which the plant itself has stored
carbohydrates for its own use. By far the most important
staple foods are the grains—wheat, rice, maize, barley,
and the sorghums, all of which belong to the grass family
and are discussed in Part IV of this volume (page 207).
Aside from the grains, probably the mostimportant starchy
food plant, at least for the white race, is the white potato
(miscalled Irish potato, for it came from America). The
white potato is not a root but a stem (see page 67). The
sweet potato (also from America), widely cultivated in
warm regions, is a true root.

Because they contain protein, the beans (legume family)
are extensively used. Numerous varieties of the navy, or
kidney, bean, the lima bean, originally. from South
America, the broad bean of Europe, and the soy bean of
China and Japan, are staples over the greater part of the
world. Other leguminous seeds widely used in eastern
countries, though not in especial favor with us, are the
chick pea, pigeon pea, and lentils. It was for a pottage of
lentils that the hungry Esau sold his birthright to Jacob.

The cassava (manioc, mandioc), originally from Brazil
where it is a staple food today, is now widely cultivated
for its fleshy roots. The refined starch obtained from
cassava is the tapioca of commerce. The fleshy under-
ground parts (corms or tubers) of the taro or dasheen, a
relative of the calla lily, also provide a commercially im-
portant starch, and from them the Hawaiians make their
“poi.” The breadfruit is a staple food in the East Indies

pol
L 98 |

HOW PLANTS ARE USED BY MAN

and the South Sea Islands. When cooked the large
spherical fruit tastes like fresh steamed bread. The trunk
of the sago palm furnishes a starchy pith used by the
natives of the South Sea Islands, and the refined product
comes into commerce as sago. Bananas and plantains
furnish food for millions of people in the Tropics, espe-
cially for the natives of Africa. The fruit is cooked and
eaten direct, or dried and ground into flour. In Arabia
and north Africa the date is a basic food, and the fig, fresh
or dried, is a food plant in the Mediterranean region.

The garden vegetables used for food are so numerous
that only the more important ones can be mentioned here.
The fleshy root of the beet, carrot, parsnip, radish, and
turnip, the bulb of the onion, the young stems of the
asparagus, the leaves of the cabbage, Brussels sprouts,
kale, and spinach, and the stem and undeveloped in-
florescence of cauliflower, the seed of the garden pea,
kidney, lima, scarlet runner and other beans, and the
edible pods of the kidney bean (string bean), are com-
monly used in cool regions. The fruits of the eggplant,
tomato, squash, pumpkin, and cucumber may be classed
as vegetables with regard to culinary use. The juicy
petioles of the rhubarb or pieplant furnish luscious _ pies
in spring. The leaves of lettuce, celery, and cress are used
for salad.

Edible fruits have been used for supplementary food
since the earliest times. In cool climates we have the
apple, pear, quince, peach, apricot, plum, cherry, grape
(raisins are dried grapes, currants are small seedless
raisins), raspberry, blackberry, strawberry (the fleshy
receptacle), gooseberry, currant, blueberry, cranberry,
watermelon, and muskmelon. Several important fruits
are now shipped to us from warmer regions, the pineapple,
the banana, the citrous fruits (orange, tangerine, lemon,
grapefruit, and lime), dates and figs (mostly dried). There
are many more in tropical regions.

Certain plant products might be called accessory foods.

[99 |

THE WORLD OF PLANTS

Many nuts and dried fruits are much in evidence about
Christmas time. The commoner nuts are the English
walnut, filbert, pecan, and peanut (a legume rather than
a nut), and Brazil nut. All of these are cultivated except
the’Brazil nut, which comes from the Amazon basin. The
fruit of this is a hard globular object containing several
angular seeds, the nuts of commerce.

A few plant products are used as flavors or relishes
rather than strictly as food. Such are the fleshy root of
the radish and horse-radish, and the spices—black pepper
(fruit), clove (flower bud), allspice (fruit), nutmeg (seed),
cinnamon (bark), red, or cayenne, pepper (fruit), ginger
(root), and mustard (seed).

The vanilla, a favorite flavoring material, comes from
the pod of a climbing orchid. Several flowers and fruits
furnish essential oils used in flavoring or in perfumery.
One of the best-known perfumes is attar of roses, made
from rose petals. Peppermint and pennyroyal are ex-
amples of essential oils from the mint family. Winter-
green comes from the blueberry family.

The chief vegetable oils used in the preparation of food
come from corn, olive, peanut, coconut, and cottonseed.

Drucs

Many powerful vegetable drugs owe their efficacy to
an alkaloid. Morphine, long known as a reliever of pain,
is the alkaloid of opium, which is produced from the milky
juice of the poppy. Cocaine comes from the leaves of the
coca plant, a shrub grown on the hillsides of Peru and
Bolivia. The natives of the Andes chew the leaves mixed
with a paste of ashes. The released alkaloid acts as a
stimulant. Quinine, a specific against malaria, comes
from the bark of the cinchona tree, a native of Peru, but
now widely cultivated in Ceylon, Java, and neighboring
countries. Strychnine, a violent poison, comes from the
seed (7ux vomica) of an Asiatic tree.

Some other common drugs are atropine (active principle

[ 100 |

HOW PLANTS ARE USED BY MAN

of belladonna) which comes from the roots and leaves of
the deadly nightshade; senna, from the leaves of the cassia
(legume family); aloes, from the juice of 4/oe (lily family);
ipecac, from the root of a South American vine; eucalyp-
tus oil, from the Australian eucalyptus tree; digitalis,
from the leaves of the foxglove; sarsaparilla, from the
roots of a tropical American species of greenbriar (Smilax);
sassafras, a common domestic remedy, from the bark of
the roots of the sassafras tree (eastern United States);
aconite, from the leaves of the monkshood. Caffeine is
the active principle of coffee, tea, and the kolanut. Castor
oil, the bane of our childhood, comes from the seeds of
the castor bean. Camphor is distilled from the twigs and
wood of an Asiatic tree. Hashish, or Indian hemp, is a
drug produced from the seed of the same plant that pro-
duces hemp fiber. Chaulmoogra oil, from the seeds of a
Burmese tree, has come into prominence recently be-
cause it is beneficial in the treatment of leprosy. Dr.
Joseph Rock’s search for the seed in its native habitat is
a botanical romance, because of the difficulties and dangers
involved. The tree is now being cultivated and the oil
will soon be widely available.
BEVERAGES

The three common beverages that come directly from
plants are: tea, the leaves of a shrub cultivated in China,
Japan, and India; coffee, the seeds of a small tree grown
in cool mountain regions of the Tropics of both hemi-
spheres; and cocoa, from the seed of a tree originating in
South America, but now widely cultivated. Maté, or
Paraguay tea, the leaves of a shrub, is much used in
southern South America. Alcoholic beverages are all in-
direct products of plants.

FIBERS

By far the most important fiber plant of the world is
the cotton, the commercial product being obtained from
the slender fibers that grow on the seed. The four other

[ ror |

THE WORLD OF PLANTS

important fiber plants are the flax, hemp, jute (all of
which furnish fiber from the stem), and the abaca (Manila
hemp), which furnishes fiber from the sheathing leaf-stalks.
Flax supplies a fine fiber from which linen is made; the
others supply coarse fibers used for cordage and coarse
cloth. The sisal, or sisal hemp, which is used for binding
twine for the harvesting of grain, is produced from the
leaves of a century plant grown in Yucatan. There are
many other fibers of less importance.

One of the most important inventions of modern times
is paper, for upon it is based the manufacture of books,
which has brought about the wide diffusion of knowledge.
The basis of paper is the cellulose of plants—obtained
from linen and cotton fibers and in recent years from wood
pulp, straw, and other materials. Rayon, or artificial
silk, is also a product of wood and other cellulose-con-
taining substances.

In ancient times one of the writing materials was made
from papyrus, a tall sedge growing in shallow water.

Woops

Our forests furnish a great variety of lumber for build-
ing, for furniture, and for other purposes. The conifers
are of prime importance as sources of lumber. White
pine, formerly much used, is becoming scarce and other
kinds are replacing this valuable species. Douglas fir and
redwood, of the Pacific Coast, are now shipped to all
parts of the world. For cabinet making the black walnut,
maple, oak, birch, and others are used because they take
a high polish. The tulip-tree furnishes a soft wood called
by cabinet makers yellow poplar, though it is not at all
allied to the poplars. Special purposes require special
woods, such as the ash and hickory.

Many tropical trees, such as the mahogany, ebony,
rosewood, and sandalwood, furnish hard dense wood
which takes a high polish. The greenheart from British
Guiana is used for piles in wharves and docks at seaports

[ 102 ]

HOW PLANTS ARE USED BY MAN

because it resists the action of the teredo, or shipworm.
Rattan, a climbing palm, is used in making furniture, and
the split canes are used for the seats of chairs.

DyYEs

Formerly vegetable dyes were much in use, but in recent
years they have been gradually supplanted by the arti-
ficial product. Indigo comes from the stems and leaves
of a leguminous plant grown in India; saffron from the
stigmas of a kind of crocus. The extract of the wood of
logwood, a tree of the American Tropics, furnishes a basis
for several dyes, especially blacks. Madder is made from
the root of an herbaceous plant. A common dye is ob-
tained from the extract of the heartwood of Brazilwood.

MIscELLANEOUS USEs

Tanning material is derived from oak bark, from the
mangrove, and from several other trees and bushes.

Rubber is made from the milky juice of several trees,
the most important of which is the Para rubber tree,
originally from Brazil. Some years ago rubber was pro-
duced only from the wild trees, but later the species was
brought into cultivation in the Malay States, Java, and
other places in the East. In America attempts are being
made to produce rubber from a desert bush, the guayule.
Two allied substances are gutta-percha—from the milky
juice of a Malayan tree—and chicle, the basis of chewing
gum—from the bully tree of Central America.

Tobacco, from the leaves of an American plant (Nico-
tiana) of the nightshade family, owes its effect to an alka-
loid—nicotine.

There are a few vegetable oils, especially olive oil (from
the fruit of the olive), that are used extensively in soap
making, in cookery, and as adulterants of other oils. The
meat of the coconut, when dried, is called copra, from
which is obtained coconut oil. Palm oil comes from the
African oil palm. Peanut oil and cottonseed oil have been

[ 103 ]

THE WORLD OF PLANTS

mentioned in previous paragraphs. They are among our
most important vegetable oils and are used for a variety of
purposes.

There are several plant products of commercial import-
ance that are classed in general as gums, balsams, and
resins. Gum arabic comes from the juice of an Egyptian
tree. When distilled, turpentine, from the sap of pine
trees, gives turpentine oil or spirits of turpentine; the
residue yields common rosin. Canada balsam comes from
the balsam fir. Amber is a fossil resin.

Coal is a plant product of past ages and we may there-
fore classify as plant products the great array of materials
that are derived from coal, such as gas, tar, and the
numerous coal-tar derivitives, including artificial dyes and
synthetic drugs.

Forage plants are indispensable to man since they serve
to feed domestic animals. The cultivated forage plants
belong chiefly to the grass family (see page 199) and to the
legume family. The cultivated forage legumes are the
clover and alfalfa, soy bean, velvet bean, the broad bean,
and several allied plants.

The more important economic plants, with the family
to which each belongs, the part used, and the hemisphere
in which each originated are given in the following table:

NAME FAMILY PART USED ORIGIN !
STAPLE Foops
Wheat Grass Grain
Rice do. do.
Maize do. do. A

1 Those marked ‘‘A”’ are originally from the Western Hemisphere (America). The
others are from the Eastern Hemisphere. Certain species of certain groups, such as the
plums and grapes, originated in one hemisphere, whereas other species of the same groups
originated in the other hemisphere. These groups are marked in the Origin column
“A (in part).”

[ 104 |

ee See SS ee

HOW PLANTS ARE USED BY MAN

NAME

Barley

Rye

Oats
Sorghum
Potato
Sweet-potato

Kidney bean
Lima bean

Soy bean
Cassava

Taro (dasheen)
Yam
Breadfruit
Sago

Banana

Plantain

Date

Fig
VEGETABLES

Pea

Kidney bean
Lima bean
Scarlet runner
String bean
Beet

Carrot
Parsnip
Turnip
Cabbage

FAMILY

do.
Nightshade
Morning-

glory

Mulberry
Palm

Banana
do.

Palm

Mulberry

Pea

do.

do.
Goosefoot
Parsley

do.
Mustard

do.

PART USED ORIGIN

ae
ei
os
QS
>>

Fleshy root

Seed A
do. A
do.

Fleshy root

Tuber

Fleshy root

Fruit

Starchy pith
of stem

Fruit
do.
do.

do.

Seed

do.

do.
Pod and seed
Fleshy root

p> > b> b>

NAME

Brussels
sprouts
Cauliflower

Onion
Asparagus
Spinach
Eggplant
Squash
Pumpkin
Cucumber
Tomato

Rhubarb

FRUITS

Apple

Pear
Quince
Peach
Plum
Apricot
Cherry
Raspberry
Blackberry
Strawberry

Grape
Gooseberry
Currant
Blueberry
Cranberry

THE WORLD OF PLANTS

FAMILY

Mustard
do.

Lily

do.
Goosefoot
Nightshade
Gourd

do.

do.
Nightshade
Buckwheat

Vine

Saxifrage
do.

Heath
do.

PART USED ORIGIN

Leaves
Stem and un-
developed
inflorescence
Bulb
Young stems
Leaves
Fruit
do.
do.
do.
do.
Juicy
petioles

le, A (in part)

F leshy recep- | A (in part)

tacle of fruit

Fruit A (in part)
do. A (in part)
do.
do. A
do. A

do. A (in part
A

HOW PLANTS ARE USED BY MAN

NAME

Pineapple
Orange
Tangerine
Lemon
Grapefruit
Lime
Watermelon
Muskmelon
Mango
Avocado
Banana

SALADS, SPICES

Radish
Celery
Lettuce
Horse-radish
Black pepper
Allspice
Clove
Cinnamon
Nutmeg

Red pepper
Mustard
Ginger
Vanilla

SUGARS

Cane
Beet
Maple

Corn

FAMILY

Pineapple
Rue
do.
do.
do.
do.
Gourd
do.
Cashew
Laurel
Banana

Mustard
Parsley
Aster
Mustard
Pepper
Myrtle

Nutmeg
Nightshade
Mustard
Ginger
Orchid

Grass
Goosefoot
Maple

Grass

PART USED

Fruit
do.
do.
do.
do.
do.
do.
do.
do.
do.
do.

Fleshy root
Petioles
Leaves
Fleshy root
Fruit

do.
Flower buds
Bark
Seed
Fruit
Seed
Root
Pod

Stem
Fleshy root
Sap

Seed

[ 107 ]

ORIGIN

> >

THE WORLD OF PLANTS

NAME

NUTS

English walnut
Pecan

Filbert

Peanut

Brazil nut
Chestnut
Almond
Cashew

DRUGS

Opium
Morphine
Cocaine
Quinine
Ipecac
Strychnine
Castor oil
Chaulmoogra
oil
Camphor
Hashish
Atropine

Senna

Aloes
Eucalyptus oil
Digitalis
Sarsaparilla
Sassafras
Aconite

FAMILY

Walnut

Pea

Brazil nut
Beech
Rose
Cashew

Logania

Spurge

Flacourtia
Laurel
Mulberry
Nightshade

Pea

Lily
Myrtle
Figwort
Lily
Laurel
Buttercup

PART USED ORIGIN

Milky juice
do.

Leaves
Bark
Root
Seed
do.

do.
Wood
Seed
Roots and

leaves
Leaves
Juice
Leaves

do.
Roots
Bark of root
Leaves

[ 108 |

A
A
A
A (in part)

> >

HOW PLANTS ARE USED BY MAN

NAME FAMILY PART USED ORIGIN
BEVERAGES
Coffee Madder Seed
Tea Tea Leaves
Cocoa Sterculea Seed A
FIBERS |
Cotton Mallow Fiber of seed | A (in part)
Flax Flax do. of stem
Hemp Mulberry dosar edo:
Abaca Banana do. of petioles
Sisal Amaryllis do. of leaves A
CABINET
WOODS
Mahogany Mahogany | Wood
Ebony Ebony do.
Rosewood Pea do.
Sandalwood Sandalwood do.
Rattan Palm Stem
DYES
Indigo Pea Stem and
leaves
Saffron Iris Stigmas
Logwood Pea Wood A
Madder Madder Root
Brazilwood Pea Wood A
OILS
Olive Olive Fruit
Corn Grass Seed A
Coconut Palm do. |

THE WORLD OF PLANTS

NAME FAMILY PART USED ORIGIN
Palm Palm Seed

Peanut Pea do. A
Cottonseed Mallow do. A (in part)
MISCELLANEOUS

Rubber Spurge Milky juice

Gutta-percha | Sapodilla do.

Chicle do. do. A
Tobacco Nightshade | Leaves A
Gum arabic Pea Juice

Turpentine Pine Sap A (in part)

Resin do. do. A (in part)

[110] |

SELECTED BIBLIOGRAPHY

Bower, F.O. Plants and man; a series of essays relating
to the botany of ordinary life. London, 1925.

Ganon, WituiaM F. The living plant; a description and
interpretation of its functions and structure. New
York, 1924.

Houtman, RicHarp M., anp Rospsins, WILFRED W. A
textbook of general botany for universities and
colleges. New York, 1924.

KERNER, ANTON VON MarILAUN, AND Otiver, F. W. The
natural history of plants, their forms, growth, re-
production, and distribution. Translated from the
German (Pflanzenleben) of Kerner by Oliver. 2 vols.
London, 1895.

ScutmpER, A. F. W. Plant-geography upon a physio-
logical basis. Translated from the German by
William R. Fisher. Revised and edited by Percy
Groom and Isaac Bayley Balfour. Oxford, 1903.

(ear

APPENDIX

GROUPING OF SOME BETTER-KNOWN
PLANTS BY FAMILIES

I. MonocoTyLEDONS

Tue lowermost families of the monocotyledons are the
cat-tail family, the pondweed family (with submerged
stems and leaves—but also often with floating leaves—
and small greenish inconspicuous flowers), the arrowhead
family (common marsh plants with arrow-shaped leaves
and white flowers), and the frogbit family (containing the
tape grass, with submerged tapelike leaves, common in
sluggish streams).

The grass family is rather simple in structure but is
made up of reduced (derived by evolutionary reduction
from more complex groups) rather than primitive forms
(see Part IV, page 199). An allied family includes the
sedges, which resemble grasses but differ in the floral
structure and in having three-ranked leaves and often
three-angled stems. The sedges are commonly found in
marshes, where they may form distinct zones of vegeta-
tion. This family, although large, includes few economic
species. The umbrella-sedge of greenhouses and the
papyrus of the Egyptians are examples. From the papyrus
an early kind of paper was made. The so-called grass or
“Crex” rugs are made from Carex, a kind of sedge.

The beautiful and graceful palms constitute a family
that has been recognized as a natural group since history
began. They are characteristic trees and shrubs of
tropical regions, though several species, as the cabbage

(rire)

GROUPS OF BETTER-KNOWN PLANTS

palmetto of our Southern States, extend into warm-
temperate countries, and fossil palms are found in Alaska.
The date palm of Arabia and North Africa, now grown in
California and Arizona, was early brought into cultivation
for its fruit, which is a staple food in the oases of North
Africa. The seed of the oil palm of Africa furnishes much
of the oil used in making soap. Probably the best known
palm is the coconut, familiar to the traveler in tropical
countries and to the would-be traveler, who is beguiled by
“its presence in all advertising matter depicting the delights
of warmer climes. Besides being a beautiful tree it is one
of the most useful of plants. Its leaves and wood as well
as its fruit serve a great variety of purposes. The “milk”
of the coconut is a most delicious drink. The dried meat
(copra) of the ripe nut is largely exported from tropical
countries for its oil, which is used for making soap and for
many other purposes. The rattan of commerce is the stem
of a climbing palm. The starchy pith of the sago palm is
a staple food in the South Sea Islands.

The aroids are numerous in the tropics but infrequent in
northern regions. The calla lily (see page 47) is probably
the most familiar example of this family. The showy part
is a specially modified leaf, inside of which, on the little
fleshy shaft, are the minute flowers. Other representatives
are the jack-in-the-pulpit, skunk-cabbage, sweetflag,
elephant’s-ear, and the curious climbing ceriman (Monstera
deliciosa) of greenhouses, which has large leaves perforated
with great holes.

The smallest and simplest of flowering plants are the
duckweeds, which are allied to the aroids. As they rarely
flower, their relationship to the aroids would not ordin-
arily be apparent. They are stemless plants from one-
twenty-fifth to two-fifths of an inch in diameter and float
free on the surface of still water. In summer and autumn
these plants may entirely cover the surface of ponds and
ditches. They propagate vegetatively, that is, by the

budding of one plant from another.

far:

THE WORLD OF PLANTS

The pineapple family—the bromeliads—includes many
epiphytes or air plants. One of these is the long, or
Spanish, moss, which hangs thickly from the live oak and
other trees of our Southern States. The pineapple origin-
ated in America but is now cultivated in all tropical
regions.

The lily family and the amaryllis family are closely
allied and may be considered together. Many of our
ornamental perennial herbs belong here—the narcissus
(including daffodil and jonquil), the lily-of-the-valley, the
yucca, and the century plant, besides the many kinds of
lilies and amaryllises. Members of these families among
our garden vegetables are the onion and the allied leek and
garlic, and the asparagus.

The yam family is important because it includes the
yam, a staple food for millions of people in tropical
regions. Its large starchy roots often weigh many pounds.
In this country a variety of sweet potato, belonging to an
entirely different family, is called yam.

The iris (blue flag) family is allied to the lilies, but the
flowers have three instead of six stamens and the styles
are quite remarkable, being split into three strap-shaped
divisions bending over the three sepals. On the under side
of each division is a lip, or flap, which is the true stigma.
All this peculiar construction is to aid in pollination. A
visiting insect—a bumblebee for example—pushes down
under this style division; if there be pollen on the bee’s
back it is scraped off by the flap and then the bee gets
more pollen from the anther just below the flap. To the
iris family belong the crocus and the gladiolus.

A group of families allied to one another are the bananas,
the gingers, the cannas, and the arrowroot. They all have
irregular flowers and broad thin leaves with many side
veins running from the midrib to the margin. The banana
is a treelike herb, which after bearing a bunch of fruit
dies to the ground, the stem being replaced by suckers.
The plantain, widely used for food in tropical regions, is a

[114]

GROUPS OF BETTER-KNOWN PLANTS

close relative of the banana. Another ally, grown chiefly
in the Philippines and neighboring countries, furnishes the
fiber abaca, or Manila hemp. The canna, or Indian shot,
is a familiar ornamental plant with red or yellow flowers.
The ginger of commerce comes from the rootstock of a
plant resembling the canna. Commercial arrowroot, an
easily digested form of starch used as a food for invalids,
comes from the rootstock of a similar plant.

The orchids are the most highly developed of the mono-
cotyledons. The flowers are irregular and many of them
very beautiful in shape and color. In number of species the
orchids constitute one of the two largest of the plant
families, though it is not usual to find large numbers of
individuals together. The method of pollination (page 49)
is usually complicated, and many species of orchids are so
modified that each of them is dependent on a single species
of insect for carrying its pollen. Not all the kinds have
large and showy flowers, like the Cattleya, Bulbophyllum,
Dendrobium, and others seen in our greenhouses; the
greater number have small or inconspicuous flowers, some
no larger than the head of a pin, but all of curious shape.
Many of the vast number of orchid species are epiphytes,
growing on the branches of trees in tropical regions; but
there are many that are not epiphytes and that grow
elsewhere than in the Tropics. In northeastern United
States there are eighteen genera and sixty-eight species,
all growing on the ground. The moccasin flowers, or lady’s
slippers, belonging to the genus Cypripedium (meaning
Venus’s shoe), have large saclike lips overarched and
flanked by three narrow divisions of the perianth. These
orchids—pink, yellow, and white—are found in moist
hemlock or pine woods, in sandy bogs and swamps, and
in rich woods. Several species of fringed orchids—purple,
rich yellow, and white—the rose colored Arethusa, Calo-
pogon, and Pogonzia, all of which grow in bogs and swamps
and wet woods, are exquisitely lovely in form and color.
Many of our terrestrial orchids, however, have small white

[115 ]

THE WORLD OF PLANTS

or greenish inconspicuous flowers. Only one of the great
number of orchids has come into commercial use other
than as ornamental plants; this is a species of Vanilla,
a vine of the American Tropics, which furnishes the
extract in common use for flavoring.

Il. DicoTyLEDONS

The well-marked willow family is made up of the willows
and poplars, two groups that have been recognized for
ages. The weeping willow (Salix baby lonica), which has
been introduced in our parks and cemeteries, grew by the
waters of Babylon, where the homesick Hebrews came to
bewail their captivity. The minute unisexual flowers are
without corollas and are borne in catkins, so called from
a fancied resemblance to a cat’s tail. The little gray

“pussies” that appear on some willows in early spring are
the young catkins before blooming, the fur being the soft
hairs on the numerous little bracts. Although the flowers
are rather simple in structure they appear to be reduced
forms of more highly developed families rather than truly
primitive forms like the flowers of magnolias.

The willows and poplars are woody plants, ranging from
large trees down to little heathlike forms only an inch or
two high. They are easily propagated from cuttings, but it
should be remembered that cuttings reproduce the sex,
those from staminate trees producing plants with stamens
only. If one wishes to propagate the common cottonwood
(a poplar) and objects to the numerous cottony seeds of
the pistillate tree, one should choose cuttings from a
staminate tree.

The oaks form another natural group long recognized;
the botanical name for the oak, Quercus, is the Latin name
for these trees, which were ben mentioned by Vergil.
The oaks have acorns, a fruit unlike any other.

Related to the oaks are the chestnuts and _ beeches,
which bear from one to four inconspicuous pistillate
flowers directly on the twigs and staminate flowers in

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catkins. In the oak and beech the catkins are small and
appear in spring just as the leaves are coming out, but in
the chestnut they bloom in summer, forming stiff white
fragrant fingers, conspicuous against the green leaves.
Less closely allied to these trees are the walnuts and
hickories, which have similar flowers and fruits, and the
hazelnuts (including the filberts), birches, and alders.
The two latter have minute winged nuts borne in conelike
catkins. Each of these groups is a genus, the birches and
alders form a family, and all the groups together form an
order.

Another order includes several allied groups known to us
as the elms, the mulberries, and the nettles. One of the
mulberries furnishes food for the silkworm. The mul-
berry family includes the tropical breadfruit and the figs.
There are many kinds of fig trees, but the most important
is the one that produces the fig of commerce. The rubber
plant of the hotel lobby with thick, smooth leaves is a
kind of fig. The nettle family includes the stinging nettle,
the bane of our childhood when exploring fence corners.
The stinging hairs inject a poison under the skin. Allied
to the nettles are the hop plant and the hemp.

The buckwheat family contains the grain from which
our buckwheat cakes are made and the rhubarb or pie-
plant whose juicy acid petioles furnish filling for pie.
Several weeds (the smartweeds, docks, and sorrels) and
the prince’s-feather of our gardens belong here. The little
fruits of many species of this family are shiny and tri-
angular.

The amaranths (the pigweed family) and chenopods
(the goosefoot family) are sister families in which the
flowers are small and lack petals. They contain several
common weeds (the pigweed and lamb’s-quarters), and
also the cockscomb of the garden. In some classifications
the apetalous families are placed by themselves as a sub-
division of the dicotyledons, but the tendency in modern
classification is to distribute them among the petaliferous

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families to which they are allied. The four-o’clock, be-
longing to an allied family, has no petals, but the calyx is
showy like a corolla. The bougainvillea, a common orna-
mental vine in warm regions, belongs to the same family,
but in this plant it is bracts instead of petals that form
the showy part of the inflorescence.

The pink family is well known through the pink and
the greenhouse carnations, the bouncing-bet, and the little
chickweeds.

The magnolias are thought by many botanists to be the
most primitive family of the dicotyledons. There are
several cultivated species brought from China and Japan,
which bear a profusion of large white or pink flowers in
the early spring before the leaves appear. The sepals,
petals, stamens, and pistils range from several to numerous
and are all separate from each other. The tulip-tree
belongs to this family, though its sepals are only three
and its petals six. The leaf of this tree is different from
those of all others, its broad summit looking as if cut off
with a pair of scissors.

The laurel family includes many woody plants with
aromatic wood and bark, such as the camphor tree (from
whose wood camphor is distilled), the cinnamon (whose
bark furnishes the spice), and the sassafras. Another
laurel, the avocado or alligator-pear tree, a native of
tropical America, is cultivated in southern Florida and
California, and its fruit is shipped to northern markets.
The leaves of the laurel of southern Europe were used in
Roman times to make crowns of victory.

A family allied to the laurel includes the nutmeg tree
of the East Indies, whose seeds are the nutmegs of com-
merce; the mace of commerce is the pulpy covering of the
seed. The seeds are dispersed by a kind of pigeon, which
swallows the seed with its mace, digests the pulp, and
voids the nutmeg uninjured.

The buttercups and their allies are herbs closely related
to the magnolia. Their stamens and pistils are usually

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numerous, as in the common yellow buttercup. To the
same family belong the clematis, the hepatica and wind-
flower (anemone) of our eastern woods, the marshmari-
gold, columbine, monkshood, and larkspur.

The water-lilies of our ponds are an allied family, the
flowers showing numerous parts, as in the magnolias. They
are not lilies in the modern sense at all. Long before the
Easter lily and its kind were named Lilium, the word was
used for any particularly lovely flower.

The crucifers, or mustard family, are a more natural
group than are many other plant families, because the
structure of the flowers follows a quite definite plan. The
group was recognized long before plants were classified in
any modern way. They are herbs with pungent juice.
The flowers, white or yellow (rarely pink), have four sepals,
four petals, six stamens (two of them shorter than the
others), and one pistil, which forms in fruit a two-celled
pod. The four petals spread in the shape of a cross, hence
the family name Cruciferae, or cross-bearers. To this
family belong several of our garden vegetables: the
cabbage and its derived forms—cauliflower, brussels
sprouts, kale, and kohl-rabi, all of which originated from
a wild cabbage; the turnip; the radish; the horse-radish;
and the water cress. The mustard, peppergrass, and
shepherd’s-purse are common weeds. The mustard of
commerce is made from the ground seeds of the cultivated
white mustard and black mustard.

Belonging to distinct but allied families are the barberry
and may-apple; the poppies and the bloodroot; the Dutch-
man’s-breeches and bleeding-heart; the pitcher plants; the
sundews and Venus’s-flytrap.

The saxifrage family contains the currants and goose-
berries and several ornamental shrubs, as the hydrangeas,
the mock oranges, and the deutzias.

The rose family is familiar and important. The flowers
of the common rose illustrate the structure. Inside the
calyx and usually showy corolla are numerous stamens

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and (usually) numerous pistils, as in the more primitive
magnolias; but the stamens and petals are attached to the
calyx cup, showing a higher development. A comparison
of the flowers of the strawberry, the blackberry, and the
apple show such a close similarity that they are generally
placed in this same family regardless of the differences in
general appearance (herb, shrub, and tree). Many of our
common fruits belong to this family—apple, pear, quince,
peach, plum, cherry, apricot, strawberry, raspberry, and
blackberry; also many ornamental plants, such as roses
and spireas.

The pea or legume family is a large one, the members of
which are easily recognized by the peculiar shape of the
flower. The sweet pea, the garden pea, the bean (many
kinds), the lentil, the clovers, and the alfalfa, the black
locust, and the beautiful wisteria vine are familiar mem-
bers of this family. An examination of the flowers will
show a remarkable similarity throughout; for example, the
single flower of a clover head will be seen to have essentially
the same structure as the sweet-pea flower. The fruits
also are similar (they are all pods), though differing in size.
The peanut, much cultivated for its oil and known to us
through the peanut stand, is peculiar in that the flower,
which is formed above ground, buries itself so that the
fruit develops underground. This burial, of course, is
aided in cultivation. The pod contains one to three seeds
—the “nuts” that we eat. The seed is very similar to that
of a bean; when the two halves or cotyledons are spread
apart, the little plumule or stemlet can be seen at the
base.

Members of families allied to the legumes are the gera-
nium, commonly grown as a house plant; the flax, from
the fibrous stem of which linen is made and whose seeds
(linseed) yield a valuable oil and a residue (oil cake), which
is nutritious food for cattle; the oxalis and the wood sorrel,
known for their acid, their cloverlike leaves, and for their
pods that shoot when touched; and the nasturtium of the

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GROUPS OF BETTER-KNOWN PLANTS

garden with curious peltate leaves (the stalk or petiole
growing from the center of the round blades).

The rue family is important to us because it includes
the citrous fruits. The Latin generic name, Citrus, has
given us the adjective citrous. We have also citric acid,
the acid of the citrous fruits, most abundant in the lime
and lemon; and the citron, the fruit whose rind is candied.
The citrous fruits common in our markets are the orange,
tangerine, lemon, and grapefruit. The lime is less common
but is grown in the West Indies for the production of lime
juice and citric acid. The family is represented in the
Eastern States by the prickly-ash and the hop-tree.

The spurge family contains many familiar species. The
garden croton, with its curiously mottled and variously
colored leaves ame twisted in a spiral, is commonly culti-
vated in warm regions. The seeds of the castor-oil plant,
which look absurdly like potato bugs, furnish the castor
oil used in medicine and as a lubricant. The “gourd” that
angered Jonah, because after coming up so quickly and
giving him hopes of a bit of shade it withered and died in
a night, has been identified as the castor-oil plant. It is
still planted beside primitive huts in far corners of the
world because it grows so quickly. The cassava (manihot,
mandioca) is, next to the grains and the potato, one of the
most important food plants of the world. The starchy,
fleshy roots are the parts used. Some sorts contain hydro-
cyanic acid, a deadly poison; however, this is dissipated
by cooking. The home of the cassava is Brazil, but it is
now widely cultivated in all warm regions. The edible
product of the plant comes into the American market in a
purified form as tapioca. A Brazilian tree belonging to this
family is the source of Parad rubber, now the most impor-
tant rubber of commerce. It is cultivated extensively in
the Malay region. Rubber is also obtained from plants of
other families. Some spurges of arid regions resemble
certain kinds of cactus. The Christ-thorn, or crown of

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THE WORLD OF PLANTS

thorns, which has small blood-red flowers and spiny stems,
is a spurge. Many spurges have milky juice.

The sumacs come in the cashew family. The poison ivy
and poison oak are two forms of the same species, the first
climbing on tree trunks by rootlets, the second shrubby.
The leaves have three leaflets, and the fruit is a cluster of
dry white berries. The foliage contains an oil, which
poisons the skin of many people who come in contact with
it. The red-berried species are harmless. A resin (lacquer)
commonly used in making varnish is obtained from a
Japanese species of sumac. To this family belong the
cashew nut, the pistachio nut, and the luscious mango.

Allied to the cashews is the ilex family, to which belong
our Christmas holly and the Paraguay tea (a common
beverage in South America); the maple family, including
the maples, the buckeyes, and the horsechestnuts; and
the balsam family, including the sultana and touch-me-
not of our gardens and the wild jewel weeds of wet woods,
all of which have succulent stems, irregular flowers, and
explosive pods.

The vine family includes the Virginia creeper and the
Boston vine, as well as the grapes. The grapes are a well-
recognized genus characterized by their fruits and their
tendrils. The Old World grape has been cultivated since
prehistoric times. The wine grape of Europe and the
imported table grapes belong to this species, which is also
cultivated extensively in California. The grapes of the
United States, except California, are varieties and hybrids
of a few American species. The American grapes differ
from the European in that the contents may be pinched
out from the skin (hence sometimes called “‘slip-skins’”’).
Because of the ravages of the phylloxera, a root louse
introduced from America, the European grape is now
grafted upon the roots of an American species that is
immune to the attacks of the insect. Raisins are dried
grapes of certain varieties and “currants” (originally im-

[naa

GROUPS OF BETTER-KNOWN PLANTS

ported from Corinth, Greece) are a small seedless variety
of raisin.

The basswood, linden, or limetree, belongs to a family
but poorly represented in the United States. The spokes
of the “One-hoss Shay” that lasted a century, were made
of basswood. Jute fiber used for bagging is obtained from
an allied shrub of the East Indies.

The mallow family, of which the common hollyhock of
the gardens is a good example, is distinguished by char-
acteristic flowers. These are usually showy and have a
mass of stamens arising as a conspicuous column from the
center. Of this family is cotton, which, aside from the
food plants, is probably the most important plant in the
world. The cotton fiber, an outgrowth of the seed, is re-
moved by a ginning machine. The seed itself furnishes the
well-known cottonseed oil, and, after the oil is pressed out,
a much-used fertilizer and cattle food (oil cake). The
picking of the cotton has been done by hand and is a
laborious process, but machines for picking are now com-
ing into use. Some years ago a well-known scientist in the
Bureau of Plant Industry, speaking at a meeting of
scientists of the need of a machine for picking cotton,
facetiously remarked that perhaps monkeys could be
trained to do the work. Somehow a newspaper reporter
heard of the remark and a fine story about monkeys as
cotton pickers appeared in the press. The Bureau was
soon bombarded with requests for further information as
to where these trained monkeys could be obtained—all
this much to the discomfiture of the scientist. To the
mallow family belong the hibiscus—including the Chinese
hibiscus (rose of China) and the shrub-althea (rose of
Sharon)—and other ornamental trees and shrubs as well
as okra, or gumbo, a vegetable popular in the South.

The ailanthus, or tree of heaven—a large graceful tree
introduced from Asia—the cacao (Theobroma), which is
the source of chocolate, and the kola nut belong to a
family allied to the mallows. The cacao is a large tree and

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THE WORLD OF PLANTS

bears small fragrant white flowers from adventitious buds
on the trunks and large branches. The fruit, borne
directly on the trunk and branches, is fleshy and measures
eight inches or more in length. Tea belongs to a family
not far removed.

Several interesting families, mostly tropical, intervene
between the foregoing and the violet family, of which
Viola, with a hundred or more species in the United States,
is the largest genus. The violets (which include the pansy)
form a very distinct group, the flowers, though differing in
size and color, all being readily recognized as of one
pattern. In addition to the flowers we all love, which are
pollinated by insects, very small short-stalked flowers
without petals which never open and are close-pollinated,
are produced by most of the species. These continue to
appear all summer, circles of plump seed pods being found
under the leaves or partly buried in the soil until fall.
The pods when ripe burst violently, throwing the seeds in
all directions.

Rather nearly related to the violets is the highly
specialized family of passion flowers. These beautiful
flowers, found growing in the wilds by the early padres,
were pointed out to the Indians as showing forth the Lord’s
passion. To quote Lindley, “Thus the three nails—two for
the hands, one for the feet—are represented by the stigmas;
the five anthers indicate the five wounds; the rays of glory,
or some say the crown of thorns, are represented by the
rays of the corona; the parts of the perianth represent the
Apostles, two of them absent—Peter who denied, and
Judas who betrayed our Lord; and the wicked hands of
his persecutors are seen in the digitate leaves of the plant,
and the scourges in the tendrils.” The passion flower 1s
frequently used as a motif in ecclesiastical embroidery and
decoration. Several species of passion flower grow in our
Southern States, the large purple flowers beautifying the
railway embankments of the Carolinas in places. The
fruits of some species are edible.

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GROUPS OF BETTER-KNOWN PLANTS

The begonias, belonging to a small family of tropical and
subtropical herbs, have fleshy stems, unsymmetrical
leaves—often strikingly colored—and waxy flowers. They
are favorite house plants, some of them being easily pro-
pagated from adventitious buds that develop on the leaves
from incisions.

The cactus family is a striking group, of American
origin, highly specialized and adapted to desert or semi-
desert conditions. The stems are condensed into fleshy,
succulent, usually very spiny columns, globes, or ovoid or
thick flat joints. They are protected from evaporation by
their reduced surface (most of them having no normal
leaves), and from herbivorous animals by the abundant
spines. The giant cactus of Arizona is a familiar com-
ponent of the desert scenery, its columnar stems rising to
heights sometimes as great as sixty feet. The barrel cactus
is a source of water to the hard-pressed traveler in the
desert. He cuts off the top, pounds up the pulp in the
barrel-shaped body, strains out the juice and drinks it.
The prickly-pears have thick flat joints with backwardly
barbed spines, which stick in the flesh and are difficult to
withdraw. Ranchmen of the Southwest singe off the
spines with gasoline torches in order that cattle may eat
the succulent joints, and even cultivate these plants,
singeing enough for a feed each day. The cattle hear the
torches and come running from all directions. No fences
are needed, as the cattle can not touch the plants until
they are singed. Spineless forms have been developed, but
they must be fenced and cut for fodder. The fruit of some
species—the “pear,”’ or tuna—is used for food. Another
species harbors the cochineal insect, which furnishes a
red dye. The juice of the cactus, under the name of
cactizona, is now coming into use for purifying boiler
tubes. The early explorers found the various kinds of
cactus so curious that they carried them back to Europe
from the deserts of America. The prickly-pears (Opuntia),
particularly, propagate so readily from the thick joints

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THE WORLD OF PLANTS

that they soon became established in congenial places
throughout the Eastern Hemisphere. One species occupies
great areas in the drier parts of the Mediterranean region,
and prickly-pears are a serious pest today in Australia.
The Indian fig, a species of Opuntia, is so characteristic a
feature of the landscape of Palestine that in many old
paintings portraying incidents in the life of Christ this
plant is conspicuous, though it did not appear in that
region till fifteen hundred years after the events pictured.

The families to which the pomegranate, the Brazil nut,
and the mangrove belong, are allied groups. They are all
related to the myrtle family, which comprises the euca-
lyptus trees (natives of Australia, but now grown in
California, Brazil, and elsewhere), the guava, allspice,
and cloves. Another relative of these groups is the evening
primrose family. It contains the evening primrose, whose
flowers are open during the night. Some of these flowers
have corolla tubes as much as four inches in length and
are pollinated by night-flying sphinx moths. Fuchsias
(named for an early German herbalist, Leonard Fuchs),
the beautiful house plants, belong to this family.

The parsley family (Umbelliferae) is one of the most
natural families that we have. Its members are herbs that
have furrowed, pithy stems, usually much divided leaves,
and aromatic or acrid juice. The structure of the flowers
and fruit is very similar throughout the group. The small
flowers are borne in clusters on the ends of branches that
start from about the same place, like the ribs of an um-
brella, and make flat-topped inflorescences called umbels.
Celery, carrot, parsnip, caraway, anise, coriander, and
parsley, and also poison hemlock belong to this family.

Closely related is the aralia family, which contains
English ivy, and ginseng and other medicinal plants. The
dogwoods—a small family, mostly shrubs—have given us
many ornamentals such as the flowering dogwood and
cornelian cherry.

The heath family is the first in the large division of the

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GROUPS OF BETTER-KNOWN PLANTS

dicotyledons in which the petals are united more or less
into a cup. The common European heather, the azaleas,
rhododendrons, and mountain laurel, which glorify our
mountain slopes and our gardens in spring, as well as blue-
berries, huckleberries, and cranberries, belong to this
family. The flowers of the heaths are highly specialized for
insect pollination. In the mountain laurel and some others
the stamens are set like a trigger so that, when released by
the insect’s tongue, they shoot the pollen over its body.

The cultivated primroses and cyclamen and our native
shooting-star belong to a small family, composed mostly
of herbs.

The ebony family, made up in the main of tropical trees
and shrubs, is represented in the United States by the
persimmon. Ebony wood is obtained from an allied
species.

The olive family contains our ash trees, the cultivated
lilac, and the olive. Allied families are those of the gentians
and the milkweeds, both of which have many genera in
the United States.

The morning-glory family is characterized by a flower in
which the petals are completely united to form a cup or
salver. The members of the family are mostly twining
plants and include the cypress-vine and morning-glory,
the bindweed, or wild morning-glory (a species of Convol-
vulus), and the sweet-potato (a species of [pomaea). The
sweet-potato, a native of Brazil, is now extensively grown
in warm regions throughout the world. A reduced mem-
ber of the family is the dodder, or love vine, a yellowish
parasitic vine which grows on weeds in August.

The phlox family (including the sweet William phlox),
the borage family, containing the heliotrope and forget-
me-not, and the verbenas, follow in order.

The mint family is a large natural group that has
opposite leaves, square stems, and aromatic foliage. The
two-lipped irregular flowers are pollinated for the most
part by insects that alight on the lower lip as a landing

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THE WORLD OF PLANTS

stage. Many of the mints yield essential oils, as the
peppermint, lavender, and pennyroyal; some—such as
marjoram, thyme, and sage—are savory herbs of the
kitchen garden. The scarlet sage is commonly cultivated
for ornament.

The nightshade family contains many medicinal plants,
such as belladonna, capiscum, and henbane, and several
cultivated for food. The white potato (so-called Irish
potato) is one of the important food plants of the world
and a source of starch. It originated in South America but
was early introduced into Europe. The tomato also came
from South America and was first introduced abroad as
an ornamental, but for many years it has been widely used
as a vegetable. The red or Cayenne pepper (chilies) and
sweet peppers, allied to the tomato, are also of American
origin. The eggplant came from Asia. The ground-cherry
and strawberry-tomato have berries inclosed in a bladdery
husk. Tobacco, another American plant, is now grown all
over the world for its leaves. The petunia is a garden
flower.

The figwort family, Scrophulariaceae, from its principal
genus, Scrophularia, so-called because the root of one
species was once used as a cure for scrofula, or king’s evil,
resembles the mint family in that most of its flowers have
two-lipped corollas; but the plants are not aromatic. The
common mullein belongs to this family, as do some of our
garden flowers—foxgloves, snapdragon, monkey-flower,
veronicas, pentstemons, and calceolarias.

The family to which the catalpas and trumpet creepers
belong and the broom rape family are closely related to
the figwort family.

The ribworts or plantains, widespread as weeds. in
lawns and waste ground, constitute a single family and
order, and have no near relatives living.

The madder family is very large but contains only a
few familiar plants. The Cape jasmine (Gardenia), a
fragrant shrub, and the buttonbush belong here, and two

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GROUPS OF BETTER-KNOWN PLANTS

important economic plants as well—coffee and cinchona.
From the bark of the latter is extracted quinine. Allied to
the madder family is the honeysuckle family, which in-
cludes the elderberry, the viburnums, the snowball, the
weigela, the honeysuckles, and other ornamental shrubs
and vines.

The gourd family consists mostly of herbaceous vines,
trailing on the ground or climbing by means of tendrils.
The family contains many useful plants—watermelon,
muskmelon (including the cantaloupe), cucumber, pump-
kin (or punkin), and the various kinds of squashes. The
pumpkin is of American origin and was cultivated by the
Indians at the time of the landing of the Pilgrims. The
gourds have long been cultivated for their hard-shelled
fruits, which when scraped out served for drinking cups
and receptacles. Gourds supplied American pioneers with
many conveniences, from dippers to darning eggs. They
are still in everyday use in regions remote from trade
routes. The wild cucumber or wild balsam-apple is an
ornamental vine.

In the related families of the bluebells and lobelias we
find a number of our garden favorites—bluebells, bell-
flowers, and canterbury-bells, and the lobelias, ranging
from the brilliant cardinal flower to the little blue edging
lobelia, commonly used for borders.

The last family of the series, the aster family, thought to
be the most highly developed of the dicotyledons, is also
the largest in number of species. The flowers are minute
and gathered into heads and many of them, as in the
oxeye daisy and sunflower, have inconspicuous flowers
in the middle and ray howers—that is, flowers with strap-
shaped corollas—around the edge, the whole simulating a
single flower with numerous petals. In the dandelion and
its near relatives all the flowers have strap-shaped corollas,
and in the ironweed and thistles all the flowers have tiny
vase-shaped corollas. A queer group, regarded by some as
a distinct family, is that of the ragweeds, most of which

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THE WORLD OF PLANTS

have the staminate and pistillate flowers in separate heads.
They are accused of being the chief cause of hay fever.
The cocklebur, or clotbur, of weedy pastures belongs to
this group. Although so large, the aster family, known
also as the composites, contains relatively few plants of
economic importance. Lettuce, chicory, and endive,
dandelion, salsify or oyster plant, globe artichoke (which
is the very young head of a plant closely related to the
thistle), and Jerusalem artichoke (the tuberous rootstock
of an American sunflower) add savory vegetables to our
tables. Sunflower seeds are eaten in Russia and elsewhere
and in this country are fed to chickens, besides being the
favorite food of caged parrots. Pyrethrum, from which
insect powder is made, and guayule, a source of rubber,
belong in this family, as do many of the herbs such as
tansy, boneset, snakeroot, yarrow, camomile, and arnica,
prized as home remedies by pioneer mothers far from
doctors.

Many beautiful cultivated flowers—asters, chrysan-
themums, calendula, cornflowers, coriopsis, cosmos, dahlia,
daisies, gaillardia, goldenglow, and zinnia—belong to this
family, and our wildwoods, prairies, and swamps, espe-
cially in late summer, are gorgeous with purple and gold
composites, among which the asters and goldenrods take a
prominent place. But a family so aggressive, so adaptable
to different environments that it out-numbers all others,
can not but intrude where man does not want it, and such
intruders are weeds. Dandelions, prickly lettuce, bur-
dock, devils-pitchforks or beggar-ticks, thistles, dog fennel,
ragweed, and a host more are cordially hated by the
weary gardener.

Only a small number of the 280 families of flowering
plants included in the Engler and Prantl system of
classification have been mentioned in the preceding out-
line.

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Part II

SYSTEMATIC BOTANY: ITS DEVELOPMENT
AND CONTACTS

By
Wiuiram R. Maxon

Associate Curator, Division of Plants
United States National Museum

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I

CHAPTER I

THE ORIGIN AND DEVELOPMENT OF
SYSTEMATIC BOTANY

Botany had its beginning in prehistoric time. It arose
from the practical need of distinguishing between plants
that ministered to man’s wants and those which did not—
of learning to pick out unerringly those kinds that could
serve for food or medicine, for shelter, and for weapons
or other implements. For each kind added to the cate-
gories of useful plants, scores must have been discarded
or passed by; and yet the number regarded favorably,
especially among those classed as medicinal, was very
large, if we may ; judge from our knowledge of primitive
peoples of the present day.

This special knowledge, slowly acquired by primitive
man from trial and observation and handed down orally
through untold generations, has afforded many a clue—
notably in medicine—leading eventually to the most
beneficent usage in our highly complicated modern life.
Again and again, on the strength of some such hint, we
carry out laborious exploration in distant tropical wilder-

esses, searching for the sources of useful plant products
that primitive man has brought to our attention. To this
simplest early type of plant study, crude and unorganized
from a scientific standpoint, we owe a debt beyond calcu-
lation in agriculture, medicine, horticulture, and a score
of related fields, upon which our existence in comfort and
our cultural life depend.

As a science, botany is classic and the oldest branch of
natural history. If we are to understand something of its

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SYSTEMATIC: BOTANY

present scope and especially the intimate relation which
plant taxonomy bears to the many other fields of modern
botanical research, we can scarcely avoid tracing briefly
the development of botany from its origin, as disclosed
in the earliest writings upon plant husbandry.

ARISTOTLE AND THEOPHRASTUS

In the wide field of botany, as in so many others, our
first recourse is to ancient Greece. As Hippocrates 1s
known as the “Father of Medicine,” so also the title
“Father of Natural History” is universally conferred on
Aristotle. Apart from conclusions based upon personal
observation, his sources of information were widely scat-
tered in the writings of early Greek poets and philosophers
and were found also in the dubious practices and tenets of
the rhizotomi, or root-gatherers, a half-illiterate class of
men among the Greeks, who for many centuries had fol-
lowed the occupation of preparing and selling roots and
herbs that were of medicinal repute. Many of Aristotle’s
inferences with regard to the facts of physiology and dis-
tinction of sex were inaccurate or quite mistaken; but so,
we may recall, were the inferences of many of his suc-
cessors, all the way down to recent times.

Next after Aristotle comes Theophrastus (Plate 19),
supplementing the work of his predecessor and carrying
it forward consistently to a point that has earned for him
the designation “Father of Botany.” He was born at
Eresos on the famous Aegean island Mitylene (anciently
known as Lesbos), in the year 370 B.c., and while a youth
had become, with Aristotle, a disciple of Plato in Athens.
Following Plato’s death, Theophrastus studied under
Aristotle, with whom his relationship appears to have
been not only that of favorite pupil but of devoted friend
and colleague as well, for on the latter’s death at the age
of sixty-three he received by bequest the exceedingly rich
library of his preceptor, Aristotle’s own manuscripts, and
the botanic garden which Aristotle had established at

[ 134]

PLATE 19

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ORIGIN AND DEVELOPMENT

Athens. Here during a long lifetime (he is said to have
lived to the age of 107) Theophrastus studied, wrote, and
lectured. His disciples numbered two thousand. He
composed voluminously and upon widely diverse topics,
in all more than 225 treatises, of which his two botanical
works are foremost. Of these his Historia Plantarum,
nearly complete in nine books, is the more important.
Concerning Theophrastus as the author of what Edward
Lee Greene calls the oldest distinctively botanical treatise
extant, one is tempted to quote at length, picturing his
unique position with respect to the development of true
botanical science and the setting in which he flourished.
“He writes,” says Greene, “from the midst of an ad-
vanced civilization; a state of society in which there is
much farming, extensive cultivation of the vine and olive,
fruit growing, market gardening, and cultivating of
medicinal, aromatic, and ornamentally flowering herbs,
shrubs, and trees; a time when many improved varieties
of all sorts of things have been devised through cultiva-
tion, and when it is already perfectly well known that such
improved varieties can not be depended on to come true
to seed, but may be preserved, and the stock of each in-
creased by division of roots, by cuttings, and by grafting.”
With this vast amount of horticultural knowledge, prac-
tice, and theory, and with ancient myth and “supersti-
tious fable’ Theophrastus was thoroughly acquainted,
first of all; and if, according to Greene, ‘‘as a mere annalist
he had but recorded the untaught industrial and experi-
mental botany of his period, together with that very con-
siderable vocabulary of botanical terms which then
formed a part of the Greek language, he would still have
done us an inestimable service.” Actually he did in-
finitely more, departing from stereotyped utilitarian
method and considering primarily the different kinds of
plants in relation to each other and their environment,
and plant organs and structures after the method now em-
ployed in comparative organography and morphology.

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SYSTEMATIC BOTANY

Throughout his writings there is abundant reference to
the economic uses of plants and to special plant products,
as he was dealing chiefly with plants long in cultivation
and with wild species of known utility; but his attitude
was purely philosophical. There was no restraining his
keen inquisitiveness about all vegetable life, an interest
that was mainly concerned with the study of plants for
its own sake and that led to the most acute observation of
minute structures of fruit, flower, foliage, root, stem, and
tendril, and particularly of seeds,. their structure and
germination, and the behavior of seedlings.

Theophrastus exerted a profound influence on later
botanical study and writing. Admittedly no traveler, he
naturally drew much of his information from classical and
contemporaneous sources; yet the method of treatment
was his, and much of the fact new and his own. The very
extent, thoroughness, and minuteness of his recorded ob-
servations (such as dates of fruiting and flowering, and the
effects of drought and moisture) and of his comparative
studies point unmistakably to first-hand acquaintance
with the living plants, of which a very considerable num-
ber were under cultivation in the garden bequeathed him
by Aristotle. In all, he discusses some four hundred fifty
species, ranging from truffles and seaweeds to pines,
domesticated grasses, and thistles. Of the groups that he
distinguished, upward of one hundred genera recognized
in our present-day botany books still bear the scientific
names he gave them; for example, Crataegus for the haw-
thorn, Aconitum for the well-known medicinal aconite,
Asparagus for the table vegetable known by that name,
and Aristolochia for the grotesque and fetid-flowered plant
we know as Dutchman’s pipe. Of a unique system of plant
names as something apart from the Greek language in
every-day use he appears to have had no notion. Different
plants were to bear distinct and characteristic names 1n
Greek, his mother tongue; and when in later centuries the
Latins studied botany, making the closest use of Theo-

[136]

ORIGIN AND DEVELOPMENT

phrastus’s Greek ae not only his descriptions ae very

many of his Greek plant names as well were carried over
into the newer language, and it is thus that they have
come down to us in latinized form.

OTHER GREEK AND RomAN WRITERS

Of writers upon plants in the period immediately follow-
ing Theophrastus there were very many among the Greeks,
comparatively few among the Latins. These authors,
however, were concerned chiefly with horticultural, agri-
cultural, and medical botany, and for the most part copied
or paraphrased the works of Theophrastus, adding little
to the sum of systematic knowledge, so far as can .be
made out from the fragments of their writings that are
preserved. A few names stand out preeminently. Such
are Nicander, a Greek naturalist of the second century
B.c., who wrote in verse of agriculture generally and of
drugs and poisons in particular, including the earliest
known dissertation on poisonous fungi; Cato (234-149
B.C.), whose treatise De Re Rustica, dealing with agricul-
ture, gardening, and the culture se propagation of choice
fruits, is the earliest work of the sort in Latin literature;
Varro (116-27 B.c.), versatile genius and most distin-
guished of erudite early Romans, who amid the routine
of an active military career found time to write of phil-
osophy, literary and political history, antiquities, naviga-
tion, education, language, and agriculture, the last treatise
(in dines Rooks) begun in his eightieth year; Vergil (70-
19 B.c.), foremost Gn Latin poets, whose Georgics, de-
voted to agriculture and gardening, reflect a profound
first-hand knowledge of plants greatly exceeding in
amount and extent that of any other early Roman writer;
Dioscorides, a Cilician Greek of Nero’s time (abene
$0 a.D.), learned physician and traveler, who in distinc-
tion from others of the same period added to Theo-
phrastan botany a knowledge of about one hundred medi-
cinal plants new to Greece and Rome, described them, and

[ 137 |]

SYSTEMATIC BOTANY

systematized the whole for the benefit of medical students,
becoming incidentally, as Greene remarks, “the first
master of phytography”’; and the elder Pliny (23-79 a.D.),
indefatigable Roman, jealous of every moment, whose
Historia Naturalis in thirty-seven books, includes sixteen
pertaining to botany, chiefly medical, horticultural, and
agricultural.

Pliny’s work was very largely a compilation, drawn
from the writings of Aristotle and Theophrastus, Nicander,
and Dioscorides, and contains little that is distinctly new
or of philosophic bearing, its trend being decidedly
economic and practical; yet it enjoyed high repute in
early medieval times and definitely helped to pave the
way for the beginnings of modern botany in the sixteenth
century.

Here also must be mentioned Galen (130-200 4.D.), a
Greek genius and erudite scholar, who in the annals of
early medicine is ranked second only to Hippocrates. An
accomplished linguist, from early youth he traveled widely
in the countries bordering the Mediterranean, seeking
“the most perfect knowledge of every plant anywhere in
use remedially.” Doubting the care or scrupulousness of
herb gatherers and venders, and denying the efficiency of
written descriptive comment as a means to the correct
identification of plant materials, he urged upon all
physicians the necessity of knowing the plants in nature,
their distinctive characters, and the appropriate seasons
of gathering, in order themselves to be able to differentiate
the false and the genuine in pharmacology. Accordingly,
although he wrote voluminously, his special province and
attainments were those of lecturer and teacher, his con-
tribution to descriptive botany being relatively slight.

THe RENAISSANCE

From these centuries onward to the sixteenth the record
of growth in botanical science is nearly lost, if indeed there
may be said to have been any real advance. However,

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ORIGIN AND DEVELOPMENT

following the development of printing in Europe the work
of Dioscorides was published in Greek (in 1499), and short-
ly afterward there appeared numerous versions of this in
Latin. The plants and plant products known to Dioscor-
ides numbered six hundred. These he had excellently
described, and “it was because he had described so many,
and often so well, that in after ages he came to be re-
garded as the supreme botanist,”’ his writing “‘more at-
tentively studied word by word, and that by a greater
number of erudite men, than any other book about plants
that has yet been written.”

In referring to the botanical renaissance of the sixteenth
and seventeenth centuries the term “German Fathers of
Botany” has commonly been used to designate as pioneers
a group of four famous herbalists—Brunfels, Fuchs, Bock,
and Valerius Cordus. The first two were successful
physicians, concerned primarily with medical botany, who,
realizing the state of confusion into which it had fallen,
undertook to make easy and sure the identification of
remedies by publishing new and lifelike engravings of
medicinal plants, executed from actual specimens.

In strong contrast to the efforts of Brunfels and Fuchs
stand the work and method of Bock and Cordus. Both
these men were keen students, and it was their conception
that, laying aside the misapplied descriptive matter
handed down or revived from a distant past, plants of all
kinds should now be accurately described with critical
attention to every detail, and in such a way as to be
recognizable from description alone, without recourse to
illustration.

Bock is the first of the so-called German Fathers actu-
ally to describe plants. At first he wrote in German and
for the enlightenment of German readers, dealing with
the plants familiarly at first hand, and it is owing largely
to this circumstance that his descriptions, afterwards re-
published in Latin for the benefit of scholars in other lands,
were of such high originality and excellence. His descrip-

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SYSTEMATIC BOTANY

tions were in reality word pictures, and they dealt with
many species previously unknown, sought out and
studied by him in what he terms “the great book of
Nature.” He was the first investigator of stamens and
pistils, and the first also among botanical writers to pub-
lish average dates of flowering for native plants, basing
his records on observations covering many seasons; yet
he could and did believe in the transmutation of one kind
of cereal into another, in the raising of a crop of turnips
“from very old cabbage seed sown by my own hands,”
and in the origin of orchid plants from the excreta of
birds.

Of far greater and even of epoch-marking import was
the work of Valerius Cordus, who has been called the one
botanical genius of the German Renaissance. Trained to
independent thought and research by his illustrious
father, the younger Cordus early became an indefatigable
field botanist and in the course of his ramblings dis-
covered among his native German fields and mountain
forests several hundred new species. These he elabor-
ately described, and at the same time he redescribed from
actual specimens many of the classical plants of remedial
repute. At the age of twenty-five he had already pre-
pared in Latin the manuscript of a work in four books,
called Historia Plantarum, describing in the fullest detail
446 species. He died in Italy four years later (1544),
following a period devoted to university studies and to
the most laborious exploration, often in unhealthful re-
gions. His great manuscript work, with the addition of a
fifth book, was published posthumously in 1561-63 under
the editorship of Conrad Gesner. Unfortunately, at the
insistence of a practical-minded publisher, it was em-
bellished with 280 figures taken from Bock’s Kreuterbuch,
these in part not applying to the plants so fully described
by Cordus. Asa result confusion arose; but even this has
not prevented the final recognition of Cordus as the first
great master of plant description in a modern sense, the

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ORIGIN AND DEVELOPMENT

first one indeed to draw up complete technical descrip-
tions according to a definitely formulated plan.

The descriptions written by Cordus were all based on
mature living plants in fruit or flower, or both. Commonly
the most obvious parts of each plant are discussed first,
the stem and foliage; then the reproductive parts—types
of inflorescence, modified leaf-structures associated with
the flowers, and characteristics of fruits and seeds; next
the root, with careful attention to its persistence, whether
annual, biennial, or perennial; and finally, notes on the
distinctive flavors and odors of plant parts, with relatively
scant mention of medicinal qualities. The same plan of
description was followed by Cordus both with the new
German species and with the old medicinal plants dating
back to Dioscorides, and its deliberate adoption, together
with his important contributions to a knowledge of flower
structures, marks a great advance in the method of plant
description. Though essentially conservative, Cordus in-
sisted on the regrouping of plants in natural family rela-
tionship on the basis of flower structures, as in the legumes,
the melons, and the buttercups, and he is reputed to have
been the first author since Dioscorides to establish a large
number of new genera of plants, these mostly of his own
discovery in Germany. His book thus becomes an im-
portant botanical landmark and well worthy of the
searching study to which it has latterly been subjected.

Other notable figures of this period include the English
herbalist, William Turner; Ghini, a celebrated teacher and
lecturer upon botany, with whom Cordus had studied
in Italy, and the first apparently to study botany from
dried plants and to suggest preserving them permanently
as reference specimens, attached to sheets of paper;
Conrad Gesner, Swiss physician, bibliographer, editor,
teacher, accomplished linguist, and classical scholar,
founder of perhaps the earliest zoological museum, pro-
digious writer and skillful draftsman, learned all-around
naturalist, whose great work, Historia Plantarum, to be

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SYSTEMATIC BOTANY

illustrated with nearly 1,500 drawings by his own hand,
remained unpublished at his death in middle life; John
and Caspar Bauhin, the latter’s outstanding contribu-
tion, Pinax Theatri Botanici, a descriptive treatise deal-
ing systematically with some 6,000 species, beginning
with the grasses and including many previously unde-
scribed plants, such as the lilac. In later botanical history
the influence of Bauhin’s Pizax proved important, most
of the scientific names employed by him being adopted
by Ray, Morison, and Tournefort.

Particularly to be mentioned also are the Flemish
botanist Clusius (1526-1609), Caesalpinus (1519-1603),
Lobelius (1538-1614), and Jung (1587-1657), all of whose
contributions were considerable. More and more, plants
came to be studied for their own sake and not for their
utilitarian values, and the results were continually re-
flected in new ideas of classification, these pointing a slow
but steady advance. In England there were Morison
(1620-1683) and Ray (1628-1705); in France, Tournefort
(1656-1708), who established a large number of genera.
Aside from classification, Ray was keenly interested in
the sexuality of plants, a doctrine proved experimentally
and almost contemporaneously by Camerarius, who states
explicitly that the stamens are male organs and the style
and ovary female organs.

THe Mopern ERA

There now appears on the scene Karl von Linné, better
known under his Latinized name Linnaeus (1707-1778),
a remarkable systematist (Plate 20), whose influence in
formal natural history classification has greatly exceeded
that of any other person in recent times. At the age
of twenty-three he had become curator of the Gardens
of the University of Lund. Following this he traveled for
several years in northern Europe, settling in 1741 at the
University of Upsala, where he occupied the chair of
botany during the remainder of his long and uneventful

[142]

PLATE 20

Linnaeus at the age of 67. After the painting by P. Krafft

ORIGIN AND DEVELOPMENT

life, teaching and publishing. His voluminous writings,
devoted strictly to describing and systematizing, had the
whole natural history world of that day as their field.
In botany his Genera Plantarum and Species Plantarum
are preeminent as providing for the first time a complete
structure, erected upon sound philosophical grounds, of
the plant kingdom as then known—the species briefly
and accurately described (partly by quotation of very
numerous phrase names and illustrations published by his
predecessors), the genera indicated clearly and precisely
as groups of closely related species, and a concise system
of names applied consistently to both throughout.!

It has been said that Linneaus was no investigator, and
that his work contains no evidence of new and important
discoveries; which may be admitted without detracting
from his fame as a literary craftsman and master-builder,
who brought together and dissected the published works
of earlier descriptive writers and out of the whole selected
and arranged the materials necessary to his own new
structure, “a building that was hailed as a masterpiece
both by his contemporaries and by generations of admir-
ing pupils.” The so-called sexual system of classification
adopted by Linneaus was highly artificial and led to the
erroneous close association of distantly related groups, and
this at a time when a more natural arrangement based
upon obvious traits of blood relationship was well under
way. From this standpoint the Linnaean arrangement
may fairly be called retrograde, yet it is rather idle to
speculate as to how greatly its influence may have re-
tarded the general advance. It was, at any rate, a work-
able system, one by which plants might readily be identi-

1The so-called binomial nomenclature, under which each species has a “double”
scientific name, generic and specific; that is, the genus name (such as Polypodium),
applied in common to all the members of a group of closely related species; and the
species name itself (e.g. vulgare), which is appended to the genus name and is used only
for a single species within the genus. Thus: Polypodium vulgare, a common fern of
temperate regions; Polypodium aureum, a tropical American fern with golden-chaffy

rootstocks. Both belong to the genus Polypodium, but each. has its distinctive specific
name.

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SYSTEMATIC BOTANY

fied, and so was of immense utility, even though it tended
to obscure natural relationships. Moreover, the service of
formulating and putting into universal practice the simple
binomial system of nomenclature is one that for all time
places students of natural history under deep obligation
to this keen-minded and vigorous organizer. For an in-
terpretation of the genera and species recognized by
Linnaeus we must in large part go back to the writings of
earlier authors, but we still adhere to his choice of scientific
names and retain them in common use, in so far as prac-
ticable, this in accordance with the so-called rule of
priority in binomial nomenclature—a -name-system of
which Linnaeus was the first consistent exponent.

Notwithstanding the immediate popularity of the
Linnaean system in many quarters, it was inevitable that
more natural schemes of classification should be proposed.
The first of these was offered by a famous French botanist,
Antoine Laurent de Jussieu (1748-1836), whose Genera
Plantarum (1789) proved the forerunner of our modern
understanding of plant relationships by families. This
in turn served as the basis of the classical Théorie élémen-
taire de la botanique by Augustin Pyrame de Candolle
(1778-1841), in which plant anatomy is emphasized as
the key to classification; in the last edition of this work,
brought out in 1844 under the editorship of his son
Alphonse, 213 “orders” or families of plants are de-
scribed, very much as recognized at present.

In the meantime other and diverse schemes of classifi-
cation had been advanced, as those of Endlicher, Bron-
gniart, and Lindley, and a wealth of material for study had
been flowing in continuously from the four corners of the
world. Much had been accomplished in England, largely
through the efforts of Sir Joseph Banks and the erudite
and versatile Robert Brown. Banks (1743-1820),
famous explorer, is distinguished for his wise, long-con-
tinued, and munificent support of botanical undertakings.
Accompanying Cook on his first voyage around the world

[144 ]

ORIGIN AND DEVELOPMENT

(1768-1771) he took with him Solander, a favorite pupil
of Linnaeus, and subsequently turned over all his ma-
terials to Brown, who meanwhile had published illumi-
natingly on the flora of Australia and New Zealand, fol-
lowing a four-year sojourn there. Aside from detailed
studies in varied fields of botanical science and the elabo-
rate monographic treatises for which he is famous, Brown
through his studies of the Australian vegetation in com-
parison with other regions of the Southern Hemisphere, is
credited with having laid the foundations of geographic
botany. The system of classification followed by him is
essentially the natural one of De Candolle. His death
occurred in 1858, just one year before the appearance of
The Origin of Species, by Charles Darwin.

It is almost impossible to over-rate the profound effect
of The Origin of Species in every department of natural
science and upon the progress of civilization itself. In-
deed, a recent botanical lecturer has expressed the opinion
that this book “has had a deeper and more wide-reaching
influence on the trend of human thought and endeavor
than any other that has ever come from the printing
press.” The modern science of natural history is itself
essentially an evolution from the infinitely painstaking
methods of observation and experimentation followed by
Darwin and the principles deduced by him from a study
of the phenomena of heredity, variation, and multiplica-
tion of organisms, both plant and animal.

It was Darwin’s good fortune to have for staunch
protagonists Huxley and Sir Joseph Hooker, and our own
Asa Gray. There was need of special advocacy, for, to
quote Farlow, to hold “that the variations and adapta-
tions of plants and animals were not for the benefit of
man, but for the benefit of the plants and animals them-
selves, was a dreadful heresy!’ The rapid adoption of the
Darwinian theory, despite vehement opposition in all
quarters, was in fact owing very largely to the potent

[145]

SYSTEMATIC BOTANY

influence of Hooker and Gray, whose views were at all
times temperately and moderately expressed.

Hooker himself had been appointed assistant director
of the Royal Botanic Gardens, Kew, in 1855; George
Bentham had come to the Gardens a year earlier. Both
were ardent students. Among their activities, devoted
largely to the preparation of a series of “floras” of the
British colonies, was the joint publication of the Genera
Plantarum, in three volumes (1865-1883), a monumental
work begun by Bentham, which contains descriptions in
Latin of all the genera and larger groups of flowering
plants then known. It was in effect a modification of the
Candollean system, which it may be said to have super-
seded for a time; but oddly enough, and in spite of
Hooker’s well known views upon the origin of species, it
reflected few of the evolutionary ideas that were deeply
influencing botanical science in general. Bentham, like
Louis Agassiz, had not been able to accept Darwin’s views,
and it was only after the Genera was well advanced in
publication that he came to modify his opinions regarding
the constancy of species.

In the cryptogams, or so-called flowerless plants, mean-
while, knowledge of structures and life histories had ad-
vanced steadily through the notable studies of De Bary,
Naegeli, Pringsheim, and others in the lower groups, and
of Hofmeister particularly among the ferns and fern allies.
Without discussing the details of these studies it may be
stated that there came now to be perceived a unity of plan
throughout the entire plant world—a bridging of the gap
hitherto supposed to exist between the cryptogams and
the seed plants in structure and in methods of sexual re-
production. The new discoveries of Hofmeister fitted per-
fectly the Darwinian theory of progressive evolution. At
last the vegetable kingdom was seen as one continuous
series, its earliest beginning shrouded in the obscurity of
a far distant past, very many intermediate forms (and
these often of profound importance) lost or known only as

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ORIGIN AND DEVELOPMENT

fossil remains, and the present flora itself a complex mix-
ture of varied types. Some of these types are old and
hardly changed from their primeval ancestral form;
others represent the highest peak of a temporarily suc-
cessful but now decadent line of evolution; and still others,
numerous and abundant, mark the most vigorous and
luxuriant evolutionary development of plastic stocks that
have proved more completely adaptable to recent condi-
tions of environment.

With the acceptance of this concept there has come a
truer realization of the extent and difficulty of the prob-
lem of classification. The account here given has indi-
cated some of the halting steps by which early botanical
knowledge progressed from a mixed basis of myth and
utilitarian practice to true botanical inquiry as a science
at the end of the Middle Ages, as well as its later in-
creasing complexity. It has dealt mainly with descrip-
tive method, as this phase of botanical study is not only
of prime importance and the first to have been developed
as a science, but is also the field with which most museums
are especially concerned. Of the essential importance of
taxonomic botany to agriculture and commerce, and to
civilization itself, more will be said in discussing its re-
lationship with the other present-day botanical sciences,
to which it stands in the closest affiliation.

[147]

CHAPTER II

THE CONTACTS AND STATUS OF
SYSTEMATIC BOTANY

Tue ultimate aim in botanical classification is to unravel
the exceedingly tangled and incomplete skein of broken
evolutionary threads, and to reconstruct the actual pat-
tern of descent. It is a task of endless extent, calling for
every bit of help that may be rendered to the taxonomist
by the paleontologist, the plant morphologist and anato-
mist, and the geneticist. Whether the system adopted
be that of Engler and Prantl, which for a generation
has generally superseded the plan of Bentham and Hooker,
or one of the more recent schemes of classification, the
end sought is the same—an orderly arrangement that
shall reflect the course of progressive evolution.

The basic service performed by systematic botany con-
sists mainly in furnishing the correct scientific names of
plants and authentic information regarding their general
and specific characteristics, their relationships, and their
geographic distribution. As the name implies, the object
of systematic botany is to provide a classification of the
different kinds of plants that together make up the earth’s
vegetation; to describe every category, bringing together
all essential data regarding structure and reproduction;
to do this in such a way that the resulting classification
shall indicate true inter-relationship; and finally, to pro-
vide stable scientific names, by means of which all the
categories may be readily distinguished and known gen-
erally. Undertaking to perform this service is a large

[148 |

PLATE 21

A live-forever (Echeveria gibbiflora, variety metallica), originally intro-
duced from Mexico to the Royal Botanic Gardens, Kew. It has since
become a popular plant for conservatories. By F. A. Walpole

CONTACTS AND STATUS

contract, and this for reasons that are not fundamentally
different from those met in zoology.

An ideal descriptive botany would be one written with
the living plants in hand, for in this way it should be pos-
sible theoretically to draw up complete true descriptions,
giving every minute detail as to color, form, structure,
size, and relationship of parts. For a limited region close
at hand such a course is feasible, and has sometimes been
followed. But in general this method of study is impracti-
cable, owing to the large areas usually covered in de-
scriptive treatises and the physical impossibility of bring-
ing together living examples of all plants, or of carrying
to them in field, swamp, and forest one’s preparation of
manuscript; time and expense also enter in.

Thus the greenhouse, or conservatory, becomes an ex-
ceedingly useful adjunct in the work of the plant systema-
tist. Indeed, without this aid it is scarcely possible to
carry out successful studies of certain difficult groups,
such as the orchids, live-forevers, and especially the
cactuses, which often have to be assembled from great
distances in a flowerless condition, to be described only
when they have flowered, after years of careful nurture.
These and certain other families, known collectively as
succulents, are difficult to make up into herbarium speci-
mens, so that a comparative study of living individuals
of the different species in the greenhouse is of more than
ordinary importance (Plate 21).

Most of the ferns and flowering plants, and even the
mosses, liverworts, and many of the fungi and seaweeds,
may be preserved readily as dried specimens, forming the
herbarium or hortus siccus, literally the “dried garden.”
Notwithstanding their limitations, herbarium specimens
with the aid to be derived from photographs of the living
plant, whole specimens or parts preserved in liquid, and
the study of living individuals in the greenhouse and
botanical garden, will doubtless remain the principal re-
source of the systematist. Though far from being inde-

[149 ]

SYSTEMATIC BOTANY

structible, dried specimens, if properly prepared and pre-
served with due care, are quite capable of lasting for cen-
turies. Many specimens two to three hundred years old
are extant, and there is on record the interesting case of
funeral bouquets unearthed a few decades ago by Petrie
in a Greco-Roman cemetery in the Fayum, in Egypt, in
which the specimens though exceedingly brittle had only
to be soaked in water to be rendered pliable and quite fit
for thorough examination, even as to the minutest struc-
tures. In these ancient Egyptian wreaths more than
twenty species of both wild and cultivated plants, in a
readily identifiable condition, were found.

Of course, no herbarium is complete or even approxi-
mately so. European institutions, from their longer
period of activity, have a decided advantage. For ex-
ample, the herbarium of the Royal Botanic Gardens, Kew,
with its accumulated 3,000,000 specimens or more, Of
which a large proportion have been examined critically
and annotated by generations of students, and the ex-
ceedingly rich early collections in the British Museum
(Natural History) have naturally an almost unequalled
historic value, requiring that these herbaria must be
sought and studied by investigators from all parts of the
world (Plate 22).

In America the United States National Herbarium in
Washington, under the care of the Smithsonian Institu-
tion, is the largest, and stands first perhaps in importance.
It contains well over 1,500,000 specimens of flowering
plants and ferns alone and is especially rich in material
from continental North America. Thus, of the 17,000
species of flowering plants known from the United States
and Canada, nearly all are represented; and of the 16,000
additional species of flowering plants occurring in Mexico
and Central America, probably nine-tenths are found in
its collections. Of the comparatively small European
flora (10,000 species of flowering plants, or less) about
four-fifths are represented. From the Philippines very

[150]

a ee eS ee ee

a iene aie

CONTAGTSVAND STATUS

ample series have been received, owing to the intensive
work carried out by American botanists during the past
three decades; but as to continental Asia and Africa, with
their huge phanerogamic floras of perhaps 40,000 species
each, it is a different story, probably not more than
twenty per cent being available. Of the 50,000 flowering
plants known from South America not more than thirty
per cent are represented by specimens from that exceed-
ingly diverse territory. Considering our expanding com-
merce with South American countries and the steadily
growing dependence of modern industry and civiliza-
tion upon raw plant products of many sorts from tropical
regions, an attempt is being made to remedy this last
deficiency through botanical exploration in northern
South America. Some account of these expeditions is
given in Part VIII of this volume (see page 351).

The original elements of the National Herbarium came
in the main from such sources as the United States Explor-
ing Expedition under Captain Wilkes (1838-1842), the
North Pacific Exploring Expedition (Ringgold and
Rogers), and the several govermental surveys of trans-
continental railroad routes; to which have been added vast
collections contributed over many years by various Gov-
ernment branches, particularly by the Department of
Agriculture, which at one time maintained the National
Herbarium in its own custody. As in other large herbaria
of a public character, a considerable number of collec-
tions have been received also by exchange and by pur-
chase, and large private herbaria have been acquired by
gift or bequest. Of the latter, special mention should be
made of the Charles Mohr collection, chiefly from Alabama
and the southern United States; the Curtis G. Lloyd
mycological collection of more than 50,000 specimens of
puffballs and woody fungi; the Biltmore herbarium of
southern United States plants, presented by Mrs. George
W. Vanderbilt; and the John Donnell Smith herbarium
of more than 100,000 specimens, assembled by that dis-

ease a

SYSTEMATIC BOTANY

tinguished botanist during a long life time and represent-
ing the most complete series of Central American plants
to be found in any institution. The materials thus as-
sembled, though inadequate as to plants of the Eastern
Hemisphere, are nevertheless of very special value in
studies of the North American flora, and have served as
the basis of an extensive literature.

In furtherance of the traditional policy of the Smith-
sonian Institution, botanical specimens from the National
Herbarium are lent freely to duly qualified students both
at home and abroad. The gain is mutual. Investigators
as a rule are eager to receive for study specimens and still
more specimens, large series of them—identified or un-
identified—from the widest possible areas, as affording a
broad basis for their work. On the other hand, the Insti-
tution benefits in having its specimens worked over
critically by specialists, whose findings are thus the more
easily understood and made available to resident botanists,
present and future. Of the papers prepared by members
of its own staff, many are published in general botanical
periodicals; others, together with treatises based by out-
side students on material in the National Herbarium,
appear in its own publication, issued in parts at irregular
intervals, entitled, ‘“Contributions from the U. S. National
Herbarium.” ‘This series, which has now run nearly to
thirty volumes, consists in part of technical papers relat-
ing to special groups, such as the ferns, grasses, palms, and
cactuses, and partly of whole volumes devoted to regional
floras; for example, the Botany of Western Texas, Flora
of New Mexico, Plant Life of Alabama, Flora of the State
of Washington, Useful Plants of the Island of Guam, Flora
of the Panama Canal Zone, and Trees and Shrubs of Mexico.
Similar series, dealing with results of study of their own
and of other herbaria, are issued by nearly all botanical
institutions and are widely distributed, mostly free or at
slight cost.

[152]

PLATE 22

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Main hall of the herbarium, British Museum (Natural History),

London, containing many early plant collections of great historical

importance. Courtesy of the British Museum

PLATE 23

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UNITEO STATES NATIONAL MUSEUM

A characteristic herbarium specimen, mounted on paper of standard
size, fully labeled, and stamped with National Herbarium serial number

CONTACTS AND STATUS

Uses oF THE HERBARIUM

This is how the herbarium functions: Let us suppose,
for example, that a student 1s to undertake a compre-
hensive treatise upon the clovers of the world. He turns
to the herbarium case containing pressed specimens of the
genus Trifolium, in the family Papilionaceae, located at a
point about one-half way down the line from the pines to
the asters, if the sequence of family arrangement adopted
be that of Engler and Prantl. Under Trifolium, in any
large herbarium, the student should find at least a thou-
sand tolerably complete specimens. Some of them will be
in fruit, others in flower, all of them, presumably, showing
foliage and, less certainly, habit of growth. Some—and
these not necessarily the most recently collected—will
show the nearly natural colors of flower and leaf.

The specimens have been made fast by glue or adhesive
strips to tough paper sheets of uniform size (1114 by 1614
inches, in American herbaria), and each will have its own
label, affixed at the lower right-hand corner, giving the
State or country, special locality, and precise date of col-
lection, together with the collector’s name and other per-
tinent data, such as elevation above sea level, the names
of companion plants, or notes on the plants’ surroundings,
whether found in moist rocky woods, in sunny situations
along a sandy lake shore, or elsewhere (Plate 23). In
mountainous regions altitude is commonly a point of
special importance, not only as an aid to the systematist
but to the plant geographer, who is concerned with the
range of species and the causes underlying their distri-
bution. So also the ecologist and plant morphologist will
welcome full data as to altitude, soil preference, moisture,
and exposure, since these facts may prove important in
explaining rather obvious differences in form, size, and
minor structure, which are suspected of having been
induced by environment.

Assuming that the investigator has become familiar with

[153]

SYSTEMATIC BOTANY

Trifolium through observation of the living plants “‘in the
field,” his future work will be about equally divided be-
tween a study of herbarium specimens and mastery of
what is called the literature of the subject. Rare publi-
cations may have to be borrowed for the sake of copying
or photographing important descriptions or suggestive
comment, and specimens also may be borrowed from
other institutions.

As to method of study, there are no hard and fast rules.
Ordinarily the student will first examine in detail certain
well-known species, comparing his specimens closely
with both the original and later descriptions. Having
made out the minute structures and technical points of
distinction, or “‘characters,” that are of importance in
the group, he will then probably sort out most of the
remaining specimens into tentative “species,” assigning
names to such of these as are readily associable with
earlier descriptions. Some of the species will be clean-cut
and will stand apart, sharply distinct in structural char-
acters and geographic distribution, from all other mem-
bers of the group. Others may be represented by very
large series of specimens coming from a wide area, and
these commonly are the most perplexing, requiring the
closest and most painstaking study. For example, a
species that is said to range from eastern Canada to the
Gulf of Mexico and westward may be expected to show
wide variation and to have assumed different forms in
separate areas of its extensive range, in response to in-
fluences of climate and general environment; indeed, it
will often be found to vary greatly even ina single locality.
The immediate problem is, then, to sort out all these local
and regional forms, to determine which are of major and
which of minor importance, and to arrange all members
of the series in a logical order that will indicate actual
relationship to each other.

But this is hardly more than a good beginning. What
our student does for a single clover species he must do for

[154]

CONTACTS AND STATUS

each and every species of the genus, except for those that
show no notable variations. Having at last settled to his
satisfaction the metes and bounds of the species and their
varieties, he must bring together related species into co-
herent groups and arrange the groups consistently.
Finally, having classified and named all the specimens, he
must write technical descriptions for the genus, the species,
and the minor forms, and provide a “‘key” as a means of
referring later students unerringly to each and every
category. The specimens studied should be listed after the
descriptions also, so that others may know the basis of
the work, in checking its correctness. Naturally the de-
scriptive portion of the monograph will be preceded by a
general chapter giving the objective sought, sources of
material, important historical notes relating to earlier
studies, the place of the group itself with respect to re-
lated genera, its geographic distribution, something of its
probable evolutionary development, and any necessary
notes on special structures and their usefulness and trust-
worthiness for purposes of classification.

In European countries the flora is relatively well known,
and refinements in classification are the rule, owing to a
general interest in botany and plant collecting and to the
comparatively small number of species involved. In
newly settled America, with its enormous stretches of
highly diverse territory, detailed studies of the native
flora have had to await widespread exploration and
collecting.

Type SPECIMENS

In general, herbarium specimens have a aouble value.
In the first place they serve as a sort of illustrated card
catalogue of the world’s flora, the individual dried and
mounted plants, properly classified, being immediately
available for description in systematic work, for com-
parison in the identification of new material, and for use
in providing distributional and other information to

[155 |

SYSTEMATIC BOTANY

students in related branches of botany. Like any classified
collection of objects, the herbarium is an illustrative
series. Equally, or even in greater measure, herbarium
specimens are of importance from the strictly historical
point of view. Having been studied by competent early.
botanists, whose opinions are recorded in an extensive
literature in which these very specimens are cited, they are
invaluable because they supply the irreplaceable data of
original investigations.

This last feature is of moment. Often fresh material of
a rare plant made known to science a hundred years ago
may still reasonably be sought in the distant region where
it was originally discovered; yet a recent specimen, even
though it comes from the same spot, will not have and
can never have a value equal to that of the original. The
specimen that actually serves as the basis of description
in proposing a new species is known as the “type” speci-
men, since it typifies the species, not biologically but his-
torically, in descriptive writing. Type specimens thus
constitute a court of last resort, to which recourse must
be had repeatedly in classification, for without them we
should constantly be forming erroneous concepts of species
previously described. There is no proper substitute for a
type specimen, carefully selected.

One obstacle to rapid advance in the field of descriptive
botany in America lies in the location of a large propor-
tion of type specimens in European herbaria. This results
in holding up the completion of many special studies until
there may come to the student finally an opportunity of
consulting these all-important specimens abroad. Photo-
graphs, indeed, are proving indispensable. Of great as-
sistance too are topotypes, that is, specimens collected
in series at original “type localities,” for among certain
plants that are not subject to great variation these will
sometimes provide much of the same valuable information
that may be had from the actual types.

[156]

CONTACTS AND STATUS

Tue Practica, IMporTANCE OF TAXONOMY

There was a time, less than two generations ago, when
to the layman and even to the professional in most
American institutions of learning, pretty much every-
thing botanical was comprised in taxonomy, or classifica-
tion according to relationship. With the rise of new
kinds and new methods of plant study in recent years,
and a general realization of their worth and deep interest,
systematic botany has come unfortunately to occupy a
less conspicuous place. Yet from the number and com-
plexity of the new problems brought up there exists as
never before an increasing need for just that kind of in-
formation which only the systematist can supply. If
agriculture is the basis of civilization, it is no less true
that botany in its broad sense is the principal basis of
scientific agriculture. And of all the present-day botani-
cal sciences there is not one that does not have inevitably
to turn to taxonomic botany for assistance.

Thus, in the popular fields of plant morphology, physi-
ology, and ecology, proper identification of the numerous
species under investigation is essential. In plant physi-
ology general principles of growth and organic function
may, it is true, be established, with the aid of physics and
chemistry, without knowing the correct name for the
plant studied. Yet-in the application of these to other
lines of purely scientific work and to economic problems,
it is essential to identify with precision the plant studied,
whether species, variety, or minor form. For instance, it
is very well known that of two forms appearing nearly or
quite identical to the unpracticed eye, one may be strongly
drought-resistant, the other scarcely at all so.

Similarly for the morphologist, who is concerned with
the life history of plants, their anatomy, and the internal
structure of their tissues and individual cells, or the
ecologist, who seeks to explain the ways by which plants
have adapted themselves to special surroundings, such as

[157]

SYSTEMATIC BOTANY

those of strand, swamp, and desert, it is obvious that
deductions based on studies of incorrectly named plants
will be of little value. Systematic botany provides the
identifications.

Turning to economic or applied botany, the relationship
is even closer, whether considered from the standpoint of
agriculture, horticulture and plant breeding, forestry,
pharmacology, bacteriology, or pathology.

Pharmacology is knowledge of drugs and medicines, of
which a very large proportion are of vegetable origin. To
know with utmost certainty the plants that yield these
medicinal principles, and to maintain a standard of purity
in drugs by excluding inferior substitutes therefor, de-
pendence is placed squarely upon taxonomy.

Practically all decay or putrefaction of both plant and
animal substances is caused by bacteria, which exist in
untold myriads. These single-celled microscopic plants
cause also such dread diseases as diphtheria, lockjaw,
typhoid, and tuberculosis, although, on the other hand,
many of them serve us most beneficently. Not all kinds of
bacteria may be distinguished by their form as viewed
through the microscope; yet their classification, which is
then accomplished by other methods, is none the less
necessary to assure a safe food supply, sanitation, com-
parative freedom from pestilence, and even our continued
existence on this earth.

Forestry also, whose prime object is the growing of
marketable timber and the perpetuation and increase of
timber-bearing areas, is on a strictly scientific basis; and
whether the trees to be tended and studied in every phase
are the solid stands of pine and spruce of the western
United States or the mixed associations of hardwoods pre-
vailing in tropical America, the first need will always be a
knowledge of their taxonomy—their names, character-
istics, affinities, abundance, and regional distribution.
Basic information of this kind is essential, for example, in
airplane manufacture, the production of fine furniture,

[158]

CONTACTS AND STATUS

interior fittings, and tools, and of paper and resins, not
to mention the flourishing and peculiarly American chew-
ing gum industry! (Plate 24.)

Like herbaceous plants, trees must be guarded from
fungus disease—a thoroughly practical consideration.
This is the province of the pathologist and the systematic
student of fungi. Enormous losses are caused annually by
the inroads of wood-destroying fungi, which we know as
shelf or bracket fungi, and which appear on tree trunks
that have first been injured, usually by fire, insect attack,
or mechanical agencies. A remedy must be sought through
a knowledge of their habits and life history. Yet not all
the pathologists in the world have been able to stem the
spread of the chestnut blight, a fungus of quite another
order, which since its appearance twenty-five years ago
has practically wiped out of existence a beautiful and
highly important timber tree in eastern North America.
A losing battle is being fought also against the destructive
white-pine blister rust, stretching nearly from coast to
coast. In the Tropics, cacao and coffee trees are notably
subject to fungus attack; indeed, the destruction of the
Arabian coffee industry in Java ‘and Ceylon is a classic
example of the havoc that may be wrought by the minute
parasitic fungi that we call rusts. Aside from various
remedial agencies designed to check or destroy the fungus
enemy, the solution often is sought by the introduction,
in areas of affected plants, of varieties or strains that are
resistant or even immune to attack by fungi.

The contacts of systematic botany with agriculture
are, of course, almost innumerable, and they are of out-
standing importance. So also with horticulture. The
subjects under study, with a view to increased yield, im-
provement in size or quality, disease resistance, or adapta-
bility to new or wider areas of cultivation may fall under
the head of vegetables, fruits, or field crops. As examples
there are the great citrus industry and its use of orange
relatives from all the tropics, either for cross-breeding

[159]

SYSTEMATIC BOTANY

or as tolerant and sturdy stock upon which to propagate
commercially desirable strains; studies of the cotton plant
and its relatives, involving not only classification of
numerous wild species but of a host of both Old and New
World forms that have been cultivated over a long
period of time; and similar investigations upon such field-
crop plants as sugar cane, oats, barley, wheat, and maize—
the last itself unknown as a wild plant and its very origin,
though of suspected hybridity, as yet unproven. In all
these experiments there is the same need of definite classi-
fication, of knowing certainly the name, origin, status, and
kinship of the stock in hand.

Exploration for new plants also plays a large part in
this work. In these days one may not hope to equal
Oviedo, whose writings (1536) contain the first published
records of rubber, cassava, the avocado (alligator pear),
the guava, and the sweet-potato, all of which were
brought to the attention of civilized man by the dis-
covery of America. But there is solid satisfaction in
having in our own day brought from Russia to America
the “durum” wheat, which is now sown annually to
about 6,000,000 acres of semi-arid land, yielding a crop
valued at some $90,000,000; in having introduced to the
desert valleys of California (Plate 25) the best date
varieties from all the principal date-growing regions of
the world, presaging the development of a horticultural
industry which even now is well beyond the infant stage;
in bringing to the warmer portions of the United States
from tropical American countries the avocado, which
during the past twenty-five years has rapidly won favor
as one of the finest salad fruits; in introducing into our
country a strain of Egyptian cotton that under careful
selection has developed into the now famous Pima variety
of Arizona; in bringing in as forage plants alfalfa and
Sudan grass, the latter now grown upon some 1,000,000
acres or more, with an estimated annual crop value of
over $15,000,000.

[ 160 |

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CONTACTS AND STATUS

THE Furure or Sysrematic BoTANy

It is safe to say that in the realm of general biology
there are today few indeed who in breadth of learning and
interest may be called naturalists, in the full sense of the
word. So also in botany, during the past three or four
decades we have been passing through a period of specializa-
tion that, although it has brought about an extraordinary
increase in detailed botanical knowledge, has by its very
subdivision nearly done away with “old-fashioned botany.”
The old-time botanist who knew the living plant and the
herbarium specimen, pursuing his studies from sheer love
of the subject and often as an avocation, has been dis-
placed by the professional specialist in many related
fields. In the United States, at least, taxonomy has not
kept pace with the newer subjects of cytology, ecology,
bacteriology, pathology, plant breeding, and genetics.
The botanical “ologies,” with their unsuspected wealth
of new fact, have nearly submerged systematic botany,
notwithstanding their obviously acute need of the help
it must give if in the long run they are to succeed. Natu-
rally enough, students trained at college in the newer
fields have, in the later role of professors, passed along
their preferences to younger students, and one result has
been an ever-increasing disparity in number between
those who have and those who have not a special interest
in systematic botany. Itis not clear that the end has been
reached. Obviously, specialization in botanical research will
continue, even multiply, and improvement in an almost in-
tolerable condition will come only with full recognition of
the importance of systematic botany and a realization of
the inadequate support it now receives. Moreover, the ap-
preciation must be general, and it must lead to collegiate
instruction in the principles and methods of taxonomy.

Three main charges have been made more or less seri-
ously against taxonomists during the last twenty-five
years by those engaged in other kinds of botanical work,
as indicating dissatisfaction: That taxonomists have

[ 161 |

SYSTEMATIC BOTANY

failed to agree among themselves upon rules that will
insure stable scientific names for general use in the plant
sciences; that frequently they have been more interested
in technical problems of nomenclature than in the plants
classified; and that a good many of them have drawn such
exceedingly fine distinctions between alleged “‘species”
that no one other than a specialist in taxonomy could hope
to recognize the forms described.

Of these criticisms the first is a fair one. Yet the names
actually used at different centers of botanical research are
not so diverse as often thought, and at the present time
a very sincere and determined effort is being made to
harmonize outstanding differences of opinion and prac-
tice and to agree completely upon an international code of
nomenclature, which all systematic botanists will accept
by reason of its honesty and practicability.

Nomenclature, it may be remarked, is a most important
part of taxonomy, and its rules and provisions are neces-
sarily technical, often highly so. The more troublesome
requirements are those aimed to govern the modern use of
scientific names recognized or first proposed by early
writers, notably Linnaeus, for genera and species. This
class of problems is the major bugbear of plant taxonomy,
and calls at once for the nicest technical judgment and the
fullest measure of common sense. Occasionally one cuts
the Gordian knot by discarding the scant claims of some
of the early names; but this method is not much followed,
and in consequence systematists are charged with petti-
fogging over “mere scientific names.” To a limited extent
this second criticism by the non-systematists is valid; yet
the great majority of systematic botanists are interested
primarily not in names, but in studies of the plants them-
selves, and do not deserve to be called name-tinkers.

As to the third specification, that of “splitting” species
and genera overfinely, one may reply that in systematic
botany as in politics there are conservatives and radicals,
not to mention numerous other partisans occupying the

[ 162 |

CONTACTS AND STATUS

whole intermediate range. Plants are highly variable:
Why not varying opinions regarding the constancy of
their agreement or difference, hence their status as rep-
resenting few or many species?

One likes to think that the botanical fathers of the
period from 1750 or thereabouts to the middle of the last
century, could they have foreseen some of the later difh-
culties of systematic botany, would have pursued a differ-
ent course; that they would have been at greater pains to
preserve their type specimens, for example, or at least to
describe them more fully, if they had guessed the multi-
plicity of species later to be turned up through distant
exploration. But original specimens were not invariably
kept, or if kept for a time they were not infrequently dis-
carded when better material supposed to represent the
same species was received. The four- or five-line Latin
descriptions, written perhaps with a single plant in hand,
may now apply equally to a whole group of closely related
forms since discovered—species indeed so evidently dif-
ferent from each other that all systematists, whether con-
servatives or radicals, must agree substantially as to their
distinctness. Along with this meagerness of description
there existed, of course, a general belief in the separate
creation of species, fashioned in a rigid mold. We now
know that species are legion, and that they are neither
fixed nor separately “created.” The points of difficulty
just mentioned are merely an unfortunate incubus, which
must be overcome. Gradually, for all groups of plants, a
trustworthy set of opinions backed by herbarium spect-
mens and published data will find general acceptance, as
it meets constantly the test of newly discovered fact,
satisfying the needs of workers in many fields.

As to what the future holds in store, there can be no
doubt: Systematic botany, whether or not receiving the
full support it merits, can never be superseded—as well
try to do without material standards of any sort. It
touches human existence and welfare at too many points.

[ 163 ]

SELECTED BIBLIOGRAPHY

ArBER, AGNES. Herbals; their origin and evolution.
New York, 1912.

Bower, Freperick O. Plants and man; a series of essays
relating to the botany of ordinary life. New York,
1925.

Ganone, Wiii1aM F. The living plant; a description and
interpretation of its function and structure. New
York, 1913.

GREENE, EpwarpD Lee. Landmarks of botanical history;
a study of certain epochs in the development of the
science of botany. Part I, Prior to 1562 a.p. Smith-
sonian Miscellaneous Collections, Vol. 54, No. 1.
Washington, 1909.

Harvey-Gisson, Rosert Joun. Outlines of the history
of botany. New York, 1919.

Hawks, Eviison, aND Boutcer, GeorcE S. Pioneers of
plant study. New York, 1928.

| 164 |

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Parr Lil

PLANTS OF THE SEA

By
ALBERT MANN

Diatomist, Carnegie Institution
Custodian, Section of Diatoms
United States National Museum

CHAPTER I
GENERAL CHARACTERISTICS

Few of us have failed to enter into friendship with nature’s
loveliest creations, the flowers, and most of us know some-
thing of the endless variety in form and color they display;
not so many perhaps, but still a large number, know that
their alluring beauty has been attained by elaborate
variations in structure—by the development of hundreds
of special tissues and organs. Finally, the botanist goes
a step farther and sees in them so many signs of inven-
tive genius, such a wealth of constructive skill, that ad-
miration turns into reverence and he finds that an assidu-
ous lifetime will be too short to finish their study.

In turning, therefore, to the plants of the sea there
comes to us at first an impression of monotony in them, of
sameness and crudity, in comparison with the more highly
developed land vegetation. But a more diligent study
soon changes this first impression, revealing that these
plainer-dressed relatives of the rose and violet and orchid
also have their charm—less vivid, it is true, but not less
real—and many other qualities which repay our interest
and study. For sea plants hardly less than those of the
land reveal marvels of adaptation to the life requirements
of their particular world and examples of as nicely attuned
ways of meeting the plants’ particular needs. Here, too,
are found grace and novelty of form, fragile beauty, and
rich coloring.

The plants of the sea are almost exclusively algae.
They form a group that stands low in the scale of life.
Their commoner name—seaweeds—is a poor one unless

[ 167 |

PLANTS OF THE SEA

we remember Emerson’s definition—that “a weed is a
plant whose use is not known”; for even with our present
scanty knowledge of sea life some valuable qualities are
already credited to the algae, and the new science of
oceanography is discovering many others. In fact, one or
two groups of algae undoubtedly deserve high rank among
the plants that contribute to the welfare of mankind.

We may pass over the small and unimportant group of
plants higher than the algae that are found in the sea.
These grow only in the shallow waters of bays and har-
bors; the most conspicuous of them is eelgrass (Zostera
marina), and even this is outclassed in frequency, prolific
growth, and economic importance by two of the algae—
the kelps and the diatoms.

The extreme simplicity of the algae as compared to land
plants is due to the fact that they live in a totally different
world—a world far less changeable, less rigorous, less
menacing; where day by day and century by century the
conditions of life are stable and kindly. It will pay to
look into this changelessness, for it is the key to the
strange forms and habits of the plants with which we have
to deal. Take, for example, the factor of temperature.
Throughout the year the waters of the ocean and of the
bays and estuaries filled by its tides show very little
change in temperature. The Gulf of Maine varies in this
respect from 35.6° (Fahrenheit) in February to 68° in
August, and this mainly near the surface; the Irish Sea
from 40.6° to 62.2°, and in the open Atlantic the variation
is even less. These variations are extremes, but even so,
they are as nothing compared with those met with on the
land. For example, St. Johnsbury, Vermont, has a tem-
perature of 30° below zero or lower in winter and go°
above zero or higher in summer. In other words, sea
plants may in extreme cases have to endure throughout
the year a change of 25° to 35° Fahrenheit (and the low
temperature will never be under freezing), whereas land
plants must find means to endure a variation of 120°.

[ 168 |

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PLATE 27

The brown alga Sargassum cymosum, from the coast of Florida. This
is the characteristic alga of the Sargasso Sea

GENERAL CHARACTERISTICS

Evidently the plants of the sea have less need to worry
about summer or winter clothing than have their relatives
of the land.

Although the watery world shows this greater uniform-
ity in temperature, there are differences between the
waters of the Tropics, the temperate zones, and the polar
regions, and the algae in these latitudes are correspond-
ingly different. For example, Laminaria, Fucus, and
other brown algae thrive best in cold water, while the red
algae and plants like the gulfweed, Sargassum, make their
home in the subtropics. We should find almost as distinct
flora in the different latitudes in the sea as on the land,
except for the fact that in the ocean these latitudinal
differences are broken down by the great currents that
flow like rivers across the seas and carry warm water into
cold regions and cold water into warm ones. The Gulf
Stream is only one of many powerful currents affecting
temperature. The Peru Current moves northward along
the west coast of South America and brings the cold water
of the far south clear up to the Equator and with the
water the cold-loving algae; so that we find the gigantic
brown Lessonia and Macrocystis and similar forms in lati-
tudes where they would otherwise never be. The Labrador
Current pushes the icy waters of the Arctic Seas south-
ward as far as Cape Cod, and in consequence the algae
that clothe the rocky coast of New England are northern
forms. One of the spectacles at the popular resorts along
that coast is the huge masses of brown Fucus that hang in
festoons over the rocks and toss in the waves that beat
upon them. The English algae, influenced by the Gulf
Stream, are very different from those of Labrador,
although the two countries are in the same latitude.

We may briefly mention here another influence disturb-
ing the orderly distribution of the algae, although it is
not strictly one of temperature. Depth has a consider-
able effect on the kinds of algae that grow in the sea.
There is a fixed limit below which no plant life can exist,

[ 169 ]

PLANTS OF THE SEA

for without sunlight there can be no vegetation; and
although some of the algae get along with very little, the
deeper parts of the ocean are absolutely without plants.
Lamouroux states that algae are found down to a depth
of 200 fathoms, or 1,200 feet. This figure is probably
too great, and it is certain that vigorous growth is not
found below 50 fathoms, or 300 feet. In the dim twilight
of the deeper places in the sea the color of the plants is
not less but more vivid than nearer the surface, a result
due to a greater development of chlorophyll and other
light-sensitive pigments made necessary by the reduced
supply of solar energy.

There is, too, a change in the abundance of plant life
in the sea at different periods of the year; but again, much
less on account of any variation in temperature than is the
case on land. The change is due chiefly to that annual
life cycle common to all vegetation. For plants have
their periods of rest and inaction just as animals do. Even
among land plants there are many in which growth stops
annually, in which life hibernates, later on to resume an
active existence, no matter what the thermometer has to
say about it. Consequently many of the algae are abun-
dant at one period of the year but rare or wanting at
another. Thus the vivid red Callithamnion americanum,
with feathery fronds as soft as eider down, is in its glory
on our Atlantic coast in late February and early March,
while Dictyoneurum californicum, a brown alga, hardly
appears until the autumn. But although these intru-
sions of cold water into warm regions and warm water into
cold regions invariably cause a local difference in sea
vegetation it is important to keep in mind that a¢ any one
of these places the water temperature maintains the same
constancy throughout the year which is so characteristic
of the sea and which makes the marine climate so much
more kindly than that of the land.

The same uniformity seen in temperature is found in the
character of the materials from which marine plants draw

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GENERAL CHARACTERISTICS

their life. The salinity of sea water is nearly uniform over
the entire earth, a little lower in the partly land-locked
Baltic Sea and Hudson Bay and a little higher in the
Persian Gulf and Red Sea, but with variations so slight
that they do not affect the plants’ welfare. Neither the
quantity of salt nor that of other constituents of sea
water presents any such problems to a marine plant as a
land plant has to face in the depleted fertility of its soil
and especially in the constant menace of too little or too
much water. For there are no droughts in the sea, and
therefore no Death Valleys or Deserts of Sahara. And
the food supply of the algae is borne to them by the cur-
rents that flow incessantly to where they grow.

One of the major modifying influences of plant life on
the land is the mechanical menace that they must over-
come. There is the lateral strain of winds, demanding
great strength and suppleness in plant structure; there
is the vertical strain of weight—their own weight added
- to by snow and ice. To meet these stresses we find superb
engineering shown in the structure of such land plants
as our trees; the buttressed bases, the sturdiness of their
vertical trunks, the fine tapering and elasticity of their
limbs and twigs. But such devices and qualities are not
needed beneath the sea, where the plants have almost
the same specific gravity as the water, or in the case of
some algae, even less, by reason of air bladders dis-
tributed through their tissues. An example is the well-
known gulfweed, Sargassum (Plate 27), a never-failing
curlosity to tourists, who know by the bright yellow
patches of it floating past the ship that they are in the
great Gulf Stream flowing northeastward across the
Atlantic. Such mechanical contrivances as those men-
tioned above and nearly all others are left out of the algae.
Strength is the thing least needed in marine plant life and
the one least often met with, for our idea of the stormy
rage of the ocean is literally a superficial one. In the
underlying waters not far below the foam-flecked surface

ba7i |

PLANTS OF THE SEA

of a stormy sea one may find calm and quietness, and
many a gale that wrecks a ship fails to dislodge the most
delicate seaweed growing on rocks below the surface.
Now it is very evident that plants living under such
benign and constant conditions need to be and therefore
will be very different from those that grow on the land
and are menaced by a hundred dangers which they must
prepare structurally to meet or die. For here in the home
of the algae no swift tempest or vicious gale can come;
no killing frosts and bitter winters; no lack of moisture;
no depletion of fertility; no crushing weight of ice and
snow. Thus the many structural and chemical safe-
guards which through long ages have been evolving in
land plants to fit them for the battle of life are in sea
plants superfluous and therefore omitted. Nature, though
lavish in her gifts, always gives wisely and is parsimonious
of wasteful effort. As no wise architect digs deep founda-
tions and builds massive pillars to hold up the light roof
of a summerhouse, so nature, the master architect, wastes
no time or material in unnecessary construction.
Here then we find the reason why the vegetation with
which this article deals, though rich in its variety of form
and sometimes rivaling land vegetation in its brilliant
and diverse colors, is built of soft and delicate tissues un-
known on the land—mere gossamer veils, mere satins and
laces. By reason of these very features sea plants are
fitted for their peculiar life conditions as nicely as are the
rugged oak and the supple bamboo for theirs. And here
also is the reason why the plants of the sea have changed
so little and those of the land so much since those far-oft
ages when Life first crept from its inorganic birthplace
to bask in the sun. The fossil algae that Dr. C. D.
Walcott found in the pre-Cambrian rocks of British
Columbia are twin brothers to those now living; whereas,
the ancestral vegetation that first clothed the steaming
plains and bogs of the land is strikingly dissimilar to that
which we see today. Day by day necessity has forced

[172]

PLATE 28

RIL ee

he Pacific Coast

from t

The brown alga Pelagophycus porra,

TF —.CC«O

GENERAL CHARACTERISTICS

these evolutionary changes of complexity and sturdiness
on land plants, while in the same lapse of time the sea
plants have but slowly and slightly drifted from those
archaic shapes with which they started.

Our group of plants then, models of simplicity because
of these sheltering and stable life conditions, omit, as has
been stated, most of the mechanical tissues and protective
devices that in variety and ingenuity are the wonder of
plant morphologists, and this too on precisely the same
ground that we omit today helmets and breastplates and
chain shirts, namely, because they are of no use. The
most that is done in self-defense is a storing up by a few
of the algae of distasteful substances, like iodine and bitter
salts, to discourage their being eaten by the hungry
hordes of animal life that swarm about them. All the
diverse functions of life go on with wonderful efficiency
and yet almost without organs, or better, let us say,
because the entire sea plant or any part of it 1s capable of
doing the work that its welfare calls for.

Let us take up the matter of food and its assimilation.
The land plant, say a rosebush, absorbs food and moisture
from the soil through a highly specialized root system
and various gases from the air through the complex
mechanism of its leaves; the alga performs these func-
tions throughout its entire surface, taking all its nourish-
ment directly from the sea that laves it. The rosebush,
hampered by those many struts and fibers that give to it
its necessary strength and flexibility, must convey the
raw material and the assimilated food products back and
forth from root to leaf and from leaf to its growing areas
or to places of storage, and special channels must be pro-
vided for this transportation. But the alga disperses its
raw material and transmutes it into living substance
throughout its entire body.

Or let us take life’s supreme and permanent puzzle,
reproduction. It calls for marvelous chemical and struc-
tural mechanisms among the higher plants—mechanisms

[173]

PLANTS OF THE SEA

invented by a genius far surpassing that of Edison and
which challenge our thought on every side. To form the
ovum and then effect its fertilization; to protect the grow-
ing embryo; to disperse the resultant seed into new
regions; to guard its vitality from killing cold and long
drought until better days come to woo it into sprouting
—these demand a thousand developments in tissues and
wrappings and appendages which the sea plant 1s able to
do without and still just as efficiently multiply its kind
and thrive.

An advantage of great consequence springs from this
simplicity; it is enabling biologists to find in these lowly
plants of the sea an opened door to a better understanding
of the mysteries of life. For the very complexity of vital
processes in higher organisms entangles the thought of
the student in a labyrinth, just as a visitor in a modern
watch factory becomes bewildered among the machines
that automatically turn out the screws and pins and
springs and wheels of a watch. The Bible metaphor, “A
little child shall lead them,” is most applicable to science;
it is the simple things that must reveal to us the complex.
Newton might have discovered the force of gravity from
the abstruse interactions of the planets, but he did not;
an apple told it to him; and Galileo grasped the principle
of the pendulum from the swaying of a chandelier in a
church. And in a precisely similar manner science will
draw ever nearer to an understanding of vital phenomena
through the agency of the simple living organisms in the
sea and similar ones in the fauna and flora of the land.

[174 ]

CHAPTER H
KINDS OF ALGAE

THE algae are conveniently divided into four main groups
by means of their colors; the blue-green, the green, the
brown, and the red. Taken alone, these colors are not
perfectly trustworthy guides, for both the brown and the
red algae occasionally tone down into a yellow; also a
few of the red algae are purple, and here and there a blue-
green alga will be far more green than blue. For example,
one of the red algae that sometimes grows in rapidly
flowing fresh-water streams, Batrachospermum, is not red
but a dirty yellowish brown. Still, these distinctions gen-
erally are so good and so convenient that their use is
justified.

We shall take up the most important group first, the
brown algae. These plants are world-wide in their dis-
tribution and very abundant in all zones, especially so in
temperate and polar waters. Probably they occur in
greatest abundance in the Australian section of the
Southern Seas. The brown algae are almost wholly
marine, in contrast to the green, which are especially con-
spicuous in fresh waters. Some members of the brown
group are of microscopic smallness, but most of them
are large and robust, and some of them are the longest of
all living things. Thus members of the genus Nereo-
oysas attainvanlensth of 325 to 350 feet; and) Dr.i Rv K,
Griggs states a single plant often weighs over 100 pounds.
They are very prolific along our Pacific coast, including
Alaska. The genus D’ Urvillaea does not afford individuals
of such enormous length; but their bulk and weight are

[175]

PEANTS OF THE SEA

sometimes very great, the heaviest recorded being about
soo pounds. ‘This genus reaches its highest development
in Australian waters. Around the Falkland Islands
grow huge fields of D’Urvillaea utilis, looking like thick
vegetable cables several hundred feet long. Along the
coast of Patagonia occur dense groves of an alga called
“the tree seaweed,” Lessonia fuscescens, which has a stem
10 to 12 feet high and 12 inches in circumference and
bears at the top a cluster of leafy fronds 3 inches broad
and from 2 to 3 feet long. Macrocystis, growing in the
Southern Hemisphere and frequent on the Pacific coast,
is the giant of all the algae (see Frontispiece). Authentic
records exist of specimens ranging in length from 650 to
985 feet. Many of these genera will be found illustrated
in the accompanying plates.

The brown algae imitate more closely than any other
group the forms and tissues of the higher land plants.
Their fibrous holdfasts which anchor them to the bottom
resemble true roots, but without any root function; their
long cylindrical stems correspond closely to the stalks of
land plants; and internally we find some of the cells with
intercommunicating pores, other cells modified into
primitive sieve tubes, and the whole stem when seen in
cross section showing a concentric arrangement—agreeing
in all these respects with stem structure in the far more
complex terrestrial plants. The upper parts of the brown
algae also share this parallelism. They are often pro-
fusely dissected into startlingly leaflike bodies, which are
flat and have a midrib running down the middle and
margins that are wavy or indented. One species of
Landsburgia is named quercifolia because its leafy thallus
so perfectly imitates the leaf of an oak. Yet all these
parts are composed of that simplest of all the plant tissues,
parenchym; wood-cells, bast, cork, and a dozen other
specialized tissues normally present in higher plants are
utterly lacking here. Nor do these strange resemblances
prevent all parts of the alga, its rootlike, stemlike, leaflike

[ 176 ]

RPAH 29

The brown alga Agarum Turneri, from the coast of Massachusetts

PLATE 30

The red alga Polysiphonia violacea, from Marthas Vineyard

KINDS OF ALGAE

divisions, from sharing equally in the many activities of
the living plant.

The multiplication of the brown algae is generally a
vegetative one, very slightly modified cells becoming
separated from the parent plant, starting independent
growth, and developing into adults. There is also a low
form of sexual reproduction. This takes place within
small cavities located near the surface of the plant and
among the simple cells that constitute its general struc-
ture. Within these cavities are developed certain gen-
erative tissues, called oogonia, that are egg-producing,
and others, called spermatogonia, that produce sperma-
tozoa. In some of the brown algae both the egg and the
spermatozoon are motile, in others only the latter, and in
still others neither. Sometimes both the vegetative and
the sexual methods of reproduction take place, alter-
nating one with the other; sometimes one predominates,
sometimes only one of the two takes place. This start-
ling lack of uniformity in the way a great life function is
performed by members of a single group of lowly plants 1s
most curious. It almost suggests that here we have come
upon nature in her undersea laboratory, experimenting
with different methods of reproduction in order to sub-
sequently fix upon the best one for adoption in those
higher forms to be hereafter developed on the land. But
if so, the experimenting was not finished; for some of these
crude reproductive methods of the brown algae reappear
in ferns and mosses and cycads and even in our conifers,
finally dropping out in our highest plants, the angiosperms.
As will be noted farther on, the brown algae play a very
conspicuous role in certain commercial products and exert
a powerful biological influence on certain other forms of
sea life.

Only a little needs to be said of the green or the blue-
green algae, because, although coordinate as groups with
the browns and reds, they play a trivial role in the econ-
omy of marine life. A few exceptional cases should be

Geral

PLANTS OF THE SEA

mentioned. There is a minute blue-green alga called
Chroococcus, barely larger than a pin point, which some-
times appears with suddenness and in startling numbers
on the surface of the sea. Four to five years ago samples
of this alga were received by me from Dr. Hugh M. Smith
at Bangkok, Siam, with a statement that the Gulf of
Siam seemed to be colored by this plant over hundreds
of square miles of surface. Then there is the interesting
green alga, “‘sea lettuce,” Ulva, looking like a leaf of that
garden vegetable or a translucent sheet of bright green
tissue paper. It is common along the northern Atlantic
seaboard in quiet coves and among piling. It has a close
relative, called Porphyra, in which the green color is
hidden by an overlying pigment of rich purple and which
has a surface that glimmers like fine satin. Then, too,
there is the dainty umbrellalike Acetabularia, its green
color softened to that of chrysoprase by an incrustation
of lime, a fragile and graceful plant. It is beautifully
illustrated in Plate 34.

The red algae are far less robust than the brown and
generally are much smaller. They usually develop into
profusely branched tufts or feathery filaments (Plate 30),
a form which has earned for them the name of “sea-
mosses.” Because of this complexity of form and a very
specialized mode of reproduction they are ranked as the
highest group of all the algae. Their tendency to elabor-
ateness is seen also in the large number of genera and
species into which they have developed. They grow best
where the boisterous pounding of the waves is broken
by the more sturdy kelps, living epiphytically among
their fronds or on rocks behind a protecting curtain of
kelp. They find a congenial home in sheltered tidal pools
and harbors. Thus, the splendid crimson Dasya elegans,
shown in Plate 34, grows abundantly in New York
harbor.

In this group are to be found most of the favorite algae
of collectors and no other members of the plant world are

[178 ]

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PLATE

ae from subtropical waters

Three coral-like red

KINDS OF ALGAE

so perfectly adapted to supply one with beautiful and
permanent specimens. Their delicate fronds, when prop-
erly arranged on cardboard, look like fine etchings; and
their soft or vivid colors rarely fade. In the extensive
herbarium of the National Museum are hundreds of these
frail children of the sea, gathered fifty years or more ago,
yet as fresh and lifelike as if the surf had just dropped
them on the shore. Some of these were used as models
by the artist, Mr. E. Cheverlange, when painting the
two superb marine scenes that are reproduced in this
volume as the frontispiece and Plate 34. As will be seen
farther on, some of the red algae are a valuable source of
food for mankind in some of the wilder parts of the world.

One other subclass of red algae merits special notice—
the corallines, so called because they closely resemble
coral. They grow in dense masses of stiff, branched,
rounded stems, or with flattened fronds, or in heavy
nodular clusters like cemented gravel (Plates 31 and 32).
They are so thickly incrusted with lime that the red or
yellow plant itself is entirely hidden. This lime, of course,
is extracted by the plant from the sea water and is then
exuded to form a hard, protective armor. In a few with
flat stems, like Mastophora, this calcareous sheath is much
thinner than in the others and is confined to the older
parts of the plant. The corallines frequent temperate and
subtropical seas, particularly places where the presence
of coral reefs insures an abundance of lime in the water,
like Bermuda and the Florida Keys. As these incrusta-
tions would make the plant dangerously brittle, if not
counteracted by other characters, the menace is avoided
either by a stocky mode of growth or by flexible joints set
at intervals along the stems, a mechanical device rein-
vented by man millions of years later and used in such
parts of machinery as the transmission shaft of an auto-
mobile. Thus the typical genus, Cora/lina, has rounded
stems made up of these flexible-jointed pieces, which give
it the appearance of chains of diminutive sausage. The

[179]

PLANTS: OF THE’ SEA

lime coating of these coralline algae does not, however,
exclude the light, because, like all other chlorophyll-
bearing plants, without light, they would be unable to
assimilate their food. The corallines are not the only
incrusted algae, for some are found in other groups and are
often mistaken for true corallines.

There remains to be considered one more group of
marine plants. They are classed among the algae by
some authors and placed adjacent to them by others, but
they are so widely different from those already men-
tioned in form and in mode of life and in the importance
of the role they play in the economy of nature, that they
stand by themselves and probably deserve the highest
consideration of all sea plants. These are the diatoms
(Plates 33 and 39), almost the smallest living things on
earth, surpassed in that respect only by the bacteria. They
are so widely distributed in all the waters of the earth and
so enormously fertile that what the other algae do worthy
of our notice these minute plants do better and on a
larger scale.

They have three qualities that are quite unlike those of
anything else in the plant world: First, each diatom builds
around itself walls of crystal, made of pure transparent
silica and constructed on the general plan of a pill box
in that they have an upper and a lower half, the sides of
the one slipping over the sides of the other. But, unlike
a pill box, they are of all shapes in addition to round—
oval, elliptical, crescent-shaped, wedge-shaped, boat-
shaped, triangular, square, stellate with from five to
twenty rays—in short, of about every conceivable shape
in which perfect symmetry and graceful contour can be
combined. Then these multiform cases, which are made
by the plant and in which it is housed, are ornamented
with such astonishing varieties of design and of such in-
comparable fineness in execution that since their dis-
covery through the invention of the microscope they have
excited the unfailing wonder of all observers.

[ 180 ]

PLATE 33

VERY Cry yey
bit thd te

Living diatoms from widely separated waters. Much enlarged

KINDS OF ALGAE

The second peculiarity of diatoms is that very many
of them have the power of free locomotion, moving about
like diminutive ships, especially like ferryboats; for they
can go forward then reverse and move in the opposite
direction. It is true that the diatoms are not the only
plants with this power and that some form of motility is
the common attribute of plants in general. Thus some
of the reproductive bodies of the algae we have been con-
sidering are motile for a few hours, but the plants en-
gendering them are fixed; the corkscrew-shaped Spirillum
is motile, as are also some of the rod-shaped bacteria.
There is a genus of blue-green algae, each individual of
which, shaped like a thin rod, slowly and incessantly
bends back and forth; this habit has given the genus its
name, Oscillaria. A few of the green algae are locomotile;
Volvox globator, for example, which suddenly appears in
inland lakes and can be seen with the aid of a hand lens
rolling along through the water in a stately way. All of
us are familiar with the movements by plants of some of
their parts; for example, Desmodium gyrans, which in
strong light keeps twitching up and down some of its leaf-
lets, so that they remind one of the fishing rod of an im-
patient angler. The sprouting potato in a dark cellar
turns its pallid stem toward the light from the cellar win-
dow, and the potted plant on the window-sill leans toward
the sun, the source of its power. But the movements of
the diatoms are different from any of these, much more
active and more powerful and they continue throughout
the life of the plant.

What causes this locomotion in diatoms has long been
one of the puzzles of science and still is shrouded in un-
certainty. The swimming of the swarm spores of algae
and the planetlike rolling of Volvox are effected by deli-
cate whiplashes called flagella, or still smaller ones called
cilia, that literally row these bodies through the water.
But a diatom does not show any organs of this sort. So
far as the best microscope reveals, the diatom seems to be

{ 181 |

PLANTS OF THE SEA

a case of a sailboat without sail, a steamship without
paddle wheel or propeller. The best of many weak
guesses is that its movement is due to rhythmic undula-
tions set up by the plant in a very thin membrane covering
externally its silica walls, which, like a succession of
waves, drives the tiny plantlet forward in somewhat the
same way that its undulations enable a snake to crawl
over the ground. And this fits in with the fact that a
diatom really craw/s, rather than swims. Unless it is in
contact with some surface it 1s as helpless as a grain of
sand.

The third distinctive quality of diatoms is their mode of
nonsexual reproduction. In general, plants that multiply
by the division of an individual into two or more new
individuals generally accomplish this by the construction
of a dividing wall across from side to side of the parent,
after which the two parts thus formed separate into inde-
pendent individuals. But the diatoms separate length-
wise in what would seem to be a much less convenient
mode; and it is this which gives them their name, derived
from two Greek words dia and tomeo, meaning to cut
through. This lengthwise splitting is very effective and
rapid. It has been computed that, taking the successive
groups of descendants in the series thus produced, more
generations will result from a single diatom in one year
than all the generations of the human race since it started
out in the Garden of Eden of Moses (or Mr. Darwin).

There are approximately 8,000 species of diatoms, dis-
tributed over the entire aquatic world; no lake or river or
stream, no seashore or harbor, no square mile of the
ocean’s surface from the North Pole to the South Pole,
being without some of these remarkable plants. As one
sails over the sea or floats his canoe over some lake, he
probably does not know that millions of diatoms are in
the water about him and form a layer of rich plant life
over the entire surface of the bottom and of the sub-
merged objects beneath the water. It is their minute-

[ 182 |

PLATE 34

A composite scene of living green and red algae from the Atlantic and
Pacific oceans. Note the variety of form. The red alga is the exquisite
Dasya elegans from New York harbor. By E. Cheverlange

KINDS OF ALGAE

ness, not their infrequency that explains this. In a bucket
of sea water dipped up anywhere diatoms will be present—
sometimes by the millions—and mixed with the sand or
the mud beneath the surface will be a teeming popula-
tion of them in incalculable numbers. I have found in
a spoonful of mud dredged near the Delaware Break-
water, 153 species of these plants and many thousands
of separate individuals. They are most abundant in
the colder latitudes of the sea. They swarm in the icy
waters of the Arctic and Antarctic oceans. Though the
most gorgeous forms are to be found in the warmer
latitudes, they are less numerous there. They came
into being comparatively late in the history of our planet,
at the beginning of the Miocene epoch or a little before
that, but long after some of the higher plants in the
sea and on the land had appeared. When they did come,
however, they came with such a rush, in such enormous
numbers, and simultaneously in so many parts of the
world that they assumed at once the dominant position
they hold today as the most prolific and most important
group of the plants of the sea.

It is not the province of this article to deal with these
captivating organisms in detail, and I must ask my
readers to note their beauty of form and the marvelous
intricacy of their ornamentation as they are revealed in
the accompanying illustrations. These have been selected
almost at random, for there is such a wealth of artistic
beauty offered by diatoms that a “beauty contest”
among them sets a hard task for the judge who must
render the decision. Some additional facts about these
most important sea plants will be found in the next
chapter.

CHAPTER: Tit
USES OF THE ALGAE

From earliest times men have gone to the storehouse of
the sea for many things. The variety of its stock is vast
and the quantity thereof is almost inexhaustible. We
may assume that the earliest quest there was for food—
for the fish and mollusks that have so largely helped to
feed the human race and without which even today
millions of people would be hard pressed to eke out a liveli-
hood. The plants of the sea also have contributed to the
feeding of mankind. The time was when they were ex-
tensively used for this purpose, and in some parts of the
world they still are an important source of food supply.
But nowadays so many choice vegetables have been pro-
duced by man’s ingenuity that the algae would find few
purchasers in any of the markets of civilized lands. Only
fifty years ago, however, one could hear in the streets of
Edinburgh the cry of hucksters peddling algae. Two
genera were popular in Scotland. One, called Irish moss,
including both Chondrus crispus and C. mammillosus, is
rich in a starchlike substance from which a nutritive
jelly can be made; the other, called tangle, including
Laminaria digitata and L. saccharina, was equally popu-
lar. There is also agar-agar, Gracilaria spinosa, still
used for food in China, but especially valuable in making
gelatinous cultures for the study of bacteria. Its near
relative, Gracilaria lichenoides, known as Ceylon moss, is
sometimes used in soups. D’Urvillaea utilis even today
serves as a food supply for some of the poorer people of
Chile. laria esculenta and Iridaea edulis also are edible.

[ 184 |

USES OF THE ALGAE

From Gigartina spinosa a palatable jelly is made. Lauren-
cia pinnatifida has a pungent taste and is called “pepper
dulse.”’ Plocaria tenax, although not an attractive food,
furnishes a strong glue used by the Chinese. But perhaps
the best known of the edible algae is the plant called dulse,
Rhodymenia palmata. It is this that Longfellow intro-
duces into the complaint of his despondent hero, John
Alden, standing on the Plymouth seashore:—

“Welcome, O Wind of the East, from the caves of the
misty Atlantic,
Blowing o’er fields of dulse and the measureless
meadows of sea grass.”

Ranking next to its gift of food as a benefit to mankind
is the sea’s contribution to the fertility of the land. The
fruitfulness of the good earth must have inspired some crude
form of agriculture almost at the start of man’s eternal
struggle for food, as the vivid allegory of Genesis points
out, where we read that Adam’s first duty was to “tend
his garden.” After a time, when the virgin richness of the
land began to be depleted, the need for fertilizing became
evident. The earliest use of seaweed as a manure is hid-
den in the dim past, but its general use today in all places
bordering on the sea proves how ancient must be its em-
ployment by tillers of the soil. At the present time a
greatly enlarged appreciation of the fertilizer value of
algae has developed; and new industries for its exploita-
tion, helped by scientific investigation, are springing up.
The primitive custom of taking what the sea casts up on
its shore’ is too inefficient for present needs; and conse-
quently methods of harvesting, drying and extracting the
more useful substances from seaweeds are now being em-
ployed. They represent one of the larger aspects of the
new science of Aquiculture.

The floating fields of giant kelp along our Pacific Coast
are the center of this modern industry of seaweed col-
lecting. Flat barges are rigged at one end with modern

[185 ]

PEANTS OF THE SEA

mowing machines, the cutting blades of which are set
about four feet below the surface. Behind these, moving
inclined planes carry the cut seaweed up into a hopper.
From there it passes into a machine like a lawn mower,
which cuts it into six-inch lengths and passes it into the
hold of the barge for transportation to the factory. The
barge is pushed forward through the fields of kelp at
about four miles an hour, and cuts and stores something
like twenty-five tons of kelp an hour. But over ninety per
cent of this harvest is water, which the factory must get
rid of, and then the dried kelp is ground into a meal, or for
certain uses the more valuable fertilizing salts and other
ingredients are extracted from it.

The most important material supplied by kelp is
potash, a prime necessity for the growing of crops and of
great use in other ways. Formerly practically all our
potash was imported, mainly from Germany, the quan-
tity increasing annually until in 1913 it amounted to
975,000 tons and cost nearly fourteen millions of dollars.
But the intervention of the World War cut off this supply,
and the need of a home supply became alarmingly urgent.
So we did as our remote ancestors had done; we went
down to the bountiful sea for help. And in the floating
beds of gigantic Macrocystis, Nereocystis, and Alaria
(Plate 36) we found our supply waiting for us. Writing
on this subject, Dr. R. F. Griggs states that from seven
to twenty-six per cent of dried kelp is potash. There 1s,
however, some advantage in using the dried algae as a
fertilizer rather than the potash extracted from them;
for these plants take from the sea water other ingredients
useful in agriculture, like phosphorus and soda, and the
plants themselves lighten the soil and through their decay
increase its fertility.

Jodine is another valuable derivative from kelp, which is
used extensively in medicine, both externally and in-
ternally, and in the arts. A rather spectacular recent use
is in the treatment of goiter, concerning which a large

[ 186 |

PLATE, 35

The red alga Gigartina microphylla, from the coast of California

USES OF THE ALGAE

number of publications are appearing, issued by the
Bureau of Chemistry and Soils and several medical jour-
nals. How the lowly algae manage to extract the minute
quantity of iodine held in solution in sea water, store it up
within their tissues, and keep it there behind a thin porous
membrane is at present incomprehensible, although no
more so than how a wayside weed selectively extracts
from the soil the ingredients it most requires. The quan-
tity of iodine in dry kelp varies from a mere trace to a
third of one per cent. Other valuable products derived
from these plants are certain gelatins used in manufacture
and in the cultivation of bacteria; also phosphates, ni-
trates, a fine grade of cellulose, and a few that are less
noteworthy.

It has long since become common knowledge that there
is an accurately balanced interchange forever going on
between the animal world and the plant world whereby
each group gives to the other a different gas without
which it could not live; and so fine is the adjustment of
this exchange that the quantity of each of these two gases
—oxygen (supplied by plants to animals) and carbon
dioxide (supplied by animals to plants)—remains prac-
tically constant in our atmosphere, although numberless
tons of each gas are daily poured into the air or extracted
from it. The same process goes on in the sea. Its animal
life could not exist an hour if the oxygen ran short, and its
plants would die almost as quickly if the carbon dioxide
ran short. Bearing in mind, then, that the algae constitute
almost the sum total of marine vegetation, it is plain that
one of their chief uses is to withdraw from sea water
carbon dioxide gas, so poisonous to animal life, and sub-
stitute the life-giving oxygen.

Exactly the same organic substance accomplishes this
exchange in the algae as in the plants of the land; namely,
chlorophyll, that green, granular constituent of living
plant cells which gives its color to all vegetation and its
tone to every landscape. The chlorophyll in the algae is

[ 187]

PLANTS’OF THE SEA

usually hidden under some thin overlying pigment,
brown or red or purple; but its chemical composition is
the same as that of the chlorophyll in a maple tree or in
a stalk of wheat, and its wonder-working exchange of
gases with the aid of sunlight is performed in precisely
the same way as in terrestrial plants. The extraction of
the one gas and the expulsion of the other generally goes
on invisibly; but often when sunlight is strong one can
see fine threads of oxygen rising from the algae toward the
surface of the water in minute streams of bubbles. Often
also, in quiet pools, one finds floating patches of brown
scum and by patient watching may see other patches rising
to the surface; these are pieces of the pellicle of diatoms
that clothes the bottom of the pool, which have been
torn away and carried upward by the large amount of
oxygen gas generated by these microscopic plants. Let
us then put down to the credit of the plants of the sea a
part of that unceasing aeration of its waters whereby it is
kept in wholesome condition for the animal life that
inhabits it.

A minor use of the algae, the exact importance of which
it would be hard to determine, is found in the shelter and
protection these plants afford to the young of fish,
crustaceans, and other marine animals during the period
of their helpless infancy. Impelled by some maternal:
instinct, as wisely ordered as if it were called wisdom,
fish, crabs, lobsters, and other sea denizens generally de-
posit their eggs in quiet inlets and bays along the coast,
where the newly hatched young will not only have an
abundant supply of the food needed for their growth but
where they can find innumerable hiding places from the
eyes of their enemies. The soft, tangled fronds of the
luxuriant seaweeds become their nursery; their own
movements are obliterated by the incessant tossing and
interlacing of these plants as the waters flow among them;
and a dim, green twilight among their supple boughs,
even at noonday, adds to the obscurity and safety of

[ 188 |

TIZI[Aof JO JO1INOS quejsiodut ue SI vale SITY T
“BYSETY jo JSvVOD nee! wod{ “ssoloV J99f XIS Apavau Sulinsvou “psopnis yf viv] P vale uMOIG 9yy jo BUILURT a[suls Vv

9¢ ALV Id

BEATE Si

The red alga Polysiphonia Baileyi, trom the

coast of California

USES OF THE ALGAE

these young. To all forms of life this initial protection is
important, as we can not have the adult stages unless the
infant stages are made safe. But with some forms it is
singularly imperative. Thus, the lobster is such a ruthless
cannibal as soon as it escapes from the egg that, were the
young not hatched where they could separate and each
newly born lobster hide from its relatives and fend for
itself, the stronger members would quickly devour the
weaker until only a few or perhaps a single individual
was left to represent the family. Seaweeds, therefore, are
the great protectors of marine animal life during the
period of greatest helplessness, and on that protection
depends the ocean’s vast abundance, which is so important
a factor to mankind.

The algae constitute the basic food supply of the entire
aquatic animal world. Probably this service outweighs
any of the uses hitherto considered. Were it not for this
vegetation there could be no marine animals, every sea
would be a Dead Sea, and three-quarters of our globe
would be as lifeless as the asphalt lakes of Trinidad. For
in the marine world as in the terrestrial one, vegetation
must furnish the food for animals. Although the latter
are composed of a few of the common elements found in
the earth’s crust and in the air that envelops it—the
oxygen and nitrogen and carbon and phosphorus and
sulphur and soda and iron and a few more—although
they are at hand and abundant, no animal can feed upon
them directly or incorporate them into its body. Only a
plant can do this wonderful thing, a plant with chlorophyll,
which somehow lays hold of the thermal and chemical rays
of the sun and by means of this borrowed power gathers
up these elements, blends and weaves them into the fabric
of its own substance, and turns lifeless matter into living
and life-supplying food. This transmutation, this mighty
miracle, reenacted every moment of every year wherever
a grass blade grows, a leaf flutters in the wind, or a sea-
weed spreads its fronds from some rock in the sea, is the

[ 189 ]

PEANTS OF THE SEA

primordial necessity to every beast and bird and fish and
crawling thing on land and in the water.

Only one group among plants must be denied credit
for this great service—the fungi—degenerates that have
ceased to produce, that merely consume, that feed upon
the products of other organisms. There are very few of
the fungi in the sea flora, far fewer than on the land. Here
and there in salt marshes or far back in some sluggish
creek, where the sea water is rank with dead vegetation
and the pulse of the tides is weak, the microscope reveals
myriads of whitish threads, the degenerate fungus,
Saprolegnia. One of these ghouls, Saprolegnia ferax,
is the cause of a very destructive malady in salmon
and of a similar disease in many fish kept in tanks or
aquariums, such as the goldfish. But out in the clean
waters of the sea the plants are honest and industrious
citizens and do their share for the general welfare. So,
casting aside this exceptional case, we may say that the
algae are of high value in the economy of nature and es-
pecially in supplying the basic food material for marine
animal life.

Most of the large algae are of little use as animal food
while they are growing. They are either tough and
leathery or acrid and unpalatable; but when they die
these repellent qualities quickly disappear, and a vast
amount of nutritive organic material becomes available
for animal food. But the small algae—the greens, blue-
greens and diatoms—have high food value at all times.
It is the last named, the diatoms, that are preeminent in
this respect. Abundant in all quarters of the globe, multi-
plying with incredible rapidity apparently always in ex-
cess of the needs of the animal life that feeds on them,
rich in nourishing qualities, spread as plankton over the
surface of the sea, suspended in the water below the sur-
face, clothing the bottom except in very deep areas with
a live mantle—the diatoms stand as the great connect-
ing link between inorganic matter and the myriads of

[ 190 |

PLATE 38

The red alga Laurencia paniculata, from the coast of Florida

PLATE 39

Fossil and living diatoms. Upper: left, 4ctinoptychus annulatus, a liv-

ing diatom from the Philippines; right, 4. wittianus, a fossil from

Haiti. Lower: left, dudiscus oamaruensis, from New Zealand; right,
Lepidodiscus elegans, from Russia

USES OF THE ALGAE

living creatures in the sea. They are the true grass of the
sea, the richest pasturage of the oceans.

The majority of marine animals, especially the larger
forms, do not feed directly upon diatoms or other sea
plants but upon those smaller animal forms which in their
turn do feed on the plants. Some fish, however, are
strictly diatom feeders, as for example, the sardine, the
menhaden, and the parrot fishes; and others, such as the
herring and the mackerel, feed on diatoms during their
period of migration. Furthermore, a very large propor-
tion of all fishes are diatom eaters during their earliest
life stages, but change to animal food or a mixed diet in
adult life. All the shellfish feed mainly upon diatoms
and those minute animal forms that are associated with
them. For example, the food of the oyster is from forty
to sixty per cent diatoms.

I recently received a letter from the west coast of India
stating that the sardines once abundant there had wholly
disappeared, causing much destitution among the people
of that region. The letter inquired if a deficiency of
diatoms was the cause of this exodus and, if so, whether a
replenishing of the coastal water with diatoms from other
localities would bring back the fish. It is rather remark-
able that the facts underlying these inquiries had reached
this remote part of the world; for the close interrelation
between an abundance of fish and an abundance of food
for fish, including the diatoms, has only recently gained
the attention that its importance deserves.

A group of very small animals, the copepods, just visible
to the naked eye and looking like tiny shrimp, to which
they are related, forms the principal connecting link
between the diatoms and the fishes. It has been found
that year by year the abundance of copepods in the sea
rises or falls in accord with the abundance or scarcity of the
diatoms, their principal food. One species, Callanus fin-
marchicus, known to sailors as “‘red seed,” often colors the
water on the Grand Banks and is common elsewhere in

[191 |

PLANTS OF THE SEA

the Atlantic Ocean. I have often examined these animals
and never without finding their intestines filled with
diatoms.

We see, therefore, that the algae have had no trivial
share in feeding mankind, either directly as human food or
indirectly—and this is especially true of diatoms—as food
for marine animal life. The sea is destined to become an
increasingly bountiful provider in proportion as the
mysteries of the deep are dispelled by scientific study and
as this permits us to acquire the art of rendering efficient
our efforts to augment the sea’s mighty resources. To
show that this is no mere dreamer’s prophecy, recent ex-
periments by the United States Bureau of Fisheries and
several State commissions have proved that by proper
cultivation oyster beds will yield per acre annually a
larger return and one having a much higher nutritive
worth and a greater market value than any known crop
from an equal area of dry land.

The benefits rendered to mankind by the plants of the
sea are nowhere more conspicuously illustrated than in the
deposits of their fossil remains found in nearly every part
of the world and particularly large and abundant in the
United States. This fossil material, a long-ago deposited
source of wealth, is known as diatomaceous earth, because
it is almost entirely composed of the remains of those
minute and elegantly ornamented algae last named in the
list—the diatoms. It has been mentioned that the out-
side encasement of these plants is composed of pure
silica. This is an indestructible substance and in this re-
spect differs radically from the substances composing
the other algae, which readily decay after death and pass
back their elements to the inorganic world from which
they were taken. As a rule the individual diatoms that
compose this fossil material do not show the slightest sign
of deterioration. Their crystal walls are as perfectly pre-
served and their delicate sculpturing as uncorroded as if
thousands of years had not come and gone since they

[192]

USES OF THE ALGAE

came into being. For nothing but the uncommon hydro-
fluoric acid or hot solutions of alkali has any effect on
diatom silica. As a consequence these tiny plants, which
lived in former ages in the same enormous numbers as
they do today and grew everywhere that water and day-
light were to be found, have formed deposits of their
imperishable remains, their silica cases; and these, ac-
cumulating through long centuries, have become beds of
diatomaceous earth. From these deposits the perishable
parts of the diatoms and the organic material with which
they originally were mixed have decayed and disap-
peared, leaving a fine, powdery, colorless substance which
to the unaided eye looks like pure chalk.

We are justified in suspecting that the diatom growth
in certain parts of the world where these beds are un-
usually large must have surpassed in annual quantity
what we find today; and this because it demands so
enormous a lapse of time, figured by the present rate of
reproduction, to account for the size of the beds. It seems
hardly credible that the changes in the earth’s crust could
have permitted their continued growth in these areas
long enough to produce such beds. To take the most
striking example known at present: A bed of diatoma-
ceous earth is located at Lompoc, California, which has
an area of approximately 12 square miles and a depth of
something like 1,400 feet. Indeed the layers that contain
some diatoms far exceed this figure in combined depth,
as it refers only to those made up of the pure grade of
diatom material that has commercial value. Above and
below this pure deposit are other diatom layers, but so
mixed with sand and other ingredients that the diatomite
is relatively worthless. The hills and hollows of the Lom-
poc deposit are composed purely of diatoms, and each cubic
inch of it contains from 3,000,000 to 5,000,000 individuals.
When we think of the meaning of this in total individuals
we are dealing with a computation that simply stuns the
mind. Other beds are less extensive, but still enormous.

[193 ]

PLANTS OF THE SEA

The so-called Nottingham earth underlies a great part of
the State of Maryland, passes southward through Wash-
ington into Virginia, appears along the banks of the
Rappahannock River near Fredericksburg, is at least
thirty feet thick under most of the city of Richmond, and
thence extends southward as far as Petersburg in the same
State. Here again the numbers stun one like the distance
between us and the remotest star. Fully 150 beds of
varied size have already been located in the United
States, and great beds are known in other countries.
Oamaru, New Zealand, the island of Barbados, Sendi,
Japan, Simbirsk, Russia, Luneberg, Germany are just a
few of the hundreds of localities that have diatom beds
which are scientifically and commercially important.
The uses of this diatomaceous earth are manifold. Its
employment as a polishing material for metals, which
first made it valuable, is far less important today, be-
cause better substances, like carborundum, have replaced
it, except as a silver polish, for which, on account of its
fineness of texture, it is still extensively used. It was
also formerly used in the manufacture of dynamite, which
is simply nitroglycerin absorbed into this porous powder
and thereby rendered less dangerous to handle. But here
also other substances, like wood-meal, have largely re-
placed it. At present it is the insulating material most
extensively used for coating steam pipes and the pipes of
ice plants, for lining the walls of blast furnaces and in the
construction of other containers where either heat or cold
needs to be confined. Thousands of tons annually are
used for filtration, especially for thick liquids like oils,
varnishes, and syrups. It is a constituent of some kinds
of porcelain and enamels. It is being mixed with other
ingredients in concrete construction, both in building
and in road making. It has many other uses and new ones
are constantly being discovered. How far back some of
these uses were known and then forgotten it is hard to
say, but some of them are certainly very ancient. Thus

[194]

USES'OF THE ALGAE

we find that in 532 a.p. the Emperor Justinian directed
that, because of their remarkably light weight, bricks
made of this material be used in repairing the Church of
Saint Sophia, Constantinople.

Another benefit derived by mankind from sea plants,
possibly greater than those just mentioned in the uses
of diatomaceous earth, results from this same deposition
in enormous masses of these minute organisms. For some
of the great diatom deposits undoubtedly are the source
of a portion of the world’s supply of petroleum, which,
in the form of gasoline, is playing such a masterful and
sometimes merciless role in our modern civilized life.
Much of the world’s petroleum supply comes from animal
and higher-plant remains; that found in the southern part
of California is diatomaceous, while that in the northern
part probably is not. These tiny plants store up their
reserve food material in the form of oil (a most unusual
thing in plant life) and this fact supplies us with the con-
nection between diatoms and petroleum. It is a heavy
oil, which by analysis has been found more closely to
“esaniblle the oil of certain marine animals, such as the
dolphins, than it does any of the other vegetable oils. It
is not infrequent to find ten per cent of the bulk of a
diatom composed of this oil, and where nourishment is
unusually abundant the quantity sometimes amounts to
forty per cent. It is easy to see, therefore, that a single
bed of diatoms like that at Lompoc, 12 square miles in
area and 1,400 feet deep, would contain enough oil to fill
a lake 12 square miles in area and 140 feet deep. This
very crude computation may help us to see how these
minute plants may have contributed greatly to preparing
the way for modern civilized life. It should be added that
some of the other algae are also sources of petroleum, but
in a very much less degree. Recent investigations have
made clear that at the present time the same processes
are going on; remains of diatoms and other organisms are
collecting on the sea bottom, and these also in ages to

[195 ]

PLANTS) OF "THE SEA

come will be transformed into diatomaceous earth, coal,
petroleum, and other mineral derivatives of organic life.

In this submarine voyage into one of the many regions
where the Smithsonian Institution has sought and found
new scientific knowledge I have written my account more
as a lover of nature than as a technical scientist. If,
therefore, any of my readers wish additional information
on any particular phase of the subject, especially on the
remarkable and complex subject of reproduction in the
algae, any technical work on this branch of science will
supply the information desired.

Thomas Moore became familiar with the algae and
other creatures of the sea through the famous marine
gardens of Bermuda during his official residence in the
island; and he took from them the inspiration for one of
his loveliest verses :—

‘“‘As down in the sunless retreats of the ocean
Sweet flowers are springing no mortal can see,
So deep in my soul the still prayer of devotion,
Unheard by the world, rises silent to Thee.”

What more perfect simile could there be than this one
between our loftiest and purest emotions and the frail sea
creatures that are the theme of this article.

SELECTED BIBLIOGRAPHY *

Arxinson, GreorcE F. Monograph of the Limnaceae of
the United States. Annals of Botany, Vol. 4.
London, 1889-91.

Borcensen, F. Marine algae from the Canary Islands.
3 Parts. Copenhagen, 1927-29.

Branpt, Ropert P. Potash from kelp; U. S. Dept. Agr.
Bull. 1191. Washington, 1923.

ENGLER AND PrantL. Pflanzenfamilien, Teil 1, Abteil 2;
new ed., in press, 1928-.

HansteEeENn, B. Studien zur Anatomie und Physiologie der
Fucoideen. Pringsheim’s Jahrb. Bd. 24, 1893.
Harvey, W. Nereis Boreali-Americana. Smithsonian
Contr. Knowledge, Vol. 2, 1852, Vol. 5, 1857. Wash-

ington.

—— A manual of the British marine algae. London,
1866.

Hervey, ALpHEuS B. Sea mosses; a collector’s guide.
Boston, 1881.

KJELLERMAN, F. R. The algae of the Arctic Sea. Kongl.
Boktryck. Stockholm, 1883.

Scumitz, F. Beitrage zur Kenntnis der Florideae. Nuova
Notarisia, ser. 3-6, 1892-96. Illustrated.

SETCHELL, WILLIAM A. On classification and geographical
distribution of the Laminariaceae. Connecticut
Acad. Arts and Sciences Trans. Vol. 5, No. 9, 1893.

—— Dirrections for collecting and preserving marine
algae, Erythea, Vol. 7, No. 3.

Taytor, Wittiam R. The marine algae of Florida.
Carnegie Inst., Washington, 1928.

1 This list of reference books has been chosen chiefly for the illustrations. Most works
on this phase of botany are highly technical.

[197]

Part IV

GRASS

By
A. S. Hircucock

Principal Botanist in Charge of Systematic Agrostology
United States Department of Agriculture
Custodian, Section of Grasses
United States National Museum
and
AGNES CHASE

Associate Botanist
United States Department of Agriculture

or
+i

CHARTER

GRASSES THE BASIS OF CIVILIZATION

“He causeth the grass to grow for the cattle,” says the
Psalmist, and Moses promised the children of Israel, as
their reward if they kept the commandments of God, that
they should have “grass in their fields for their cattle.”
With the Prophets grass is the symbol of blessing and re-
demption—“‘in the habitation of dragons shall be grass,”
“the Lord shall give to everyone grass in the field.” And
the want of grass is the symbol of desolation, “‘the hay
is withered away, the grass faileth.” The theme of grazing
runs all through Genesis and Exodus. But long before
cattle were domesticated, primitive man, living largely on
animals he could kill, was vitally concerned with grazing
lands. He must have followed the herds of wild cattle and
bison, the flocks of wild sheep and goats, as the North
American Indian followed the herds of the American
bison, or buffalo. An abundant supply of grass meant
plenty of tender, juicy meat.

Grazing lands possess other plants than true grasses,
but grasses are their most important constituent, because
these plants withstand close and repeated grazing better
than do other plants. In the grass leaf, consisting of two
parts—sheath and blade—growth takes place at the base
of the sheath and at the base of the blade (Fig. 36), instead
of being diffused about equally throughout the leaf, as it is
in clovers and other forage plants. When a clover leaf is
bitten off, that is the end of it, but when a grass blade
is bitten off, growth keeps on at the base and the blade
is soon as long as ever. It is this growth from the base

Laon |

GRASS

| Se ERB eee

Fic. 36. Leaves of grass and of red clover marked
to show areas of growth. A, grass leaf: a, base of
blade; b, base of sheath. B, same leaf one week later,
showing growth at a and b. C, base of culm in
sheath; bud of potential branch shown atc. D,same
one week later, showing growth at the base and
the potential bud developed into a leafy shoot.
E, leaf of red clover. F, same one week later, show-
ing nearly uniform growth throughout, the greatest
growth taking place in the petiole, the part of least
value

i
to
O
Vv

—

THE BASIS OF CIVILIZATION

(like human hair) that makes necessary repeated mowing
of the lawn. Moreover, in a grass not only is the leaf
renewed but the stem also. A grass stem is jointed, each
joint bearing a leaf. In the axil of each leaf is a potential
bud, which lies dormant so long as the main stem is
erowing. If, however, the main stem 1s grazed or cut off,
the bud in the axil of the uppermost remaining leaf de-
velops and replaces it. Grass is nature’s nearest ap-
proach to an indestructible forage plant. So dominant
are the grasses among grazing plants that the English
word grass, which originally meant herbage in general,
and from which is derived the verb /o graze, has come to be
applied particularly to the gramina, or “‘true grasses.”

These true grasses seem to have appeared on the earth
during Upper Cretaceous time, as their earliest fossil
representatives have been found in formations laid down
in this period. In the Eocene there was a notable expan-
sion of the grass family, and in the Miocene it was well on
its way to becoming one of the dominant types of plant
life. Little Eohippus, of the Eocene, the great-great-
grandfather of all the horses, and his descendants in the
Oligocene, who have left their fossil remains in our
Western States, had teeth for eating twigs and bark.
During the Miocene our Great Plains were uplifted and
became a vast grassland. The little browsing horse, no
larger than a sheep, developed teeth for grazing, and,
living on a grass diet through many generations, in-
creased in size and swiftness until, when the Ice Age ap-
peared, there were at least ten species of the genus, some
as large as the domesticated horse of today and one even
larger. The horse and the other graminivorous (or graz-
ing) animals, the ancestors of our domestic live stock,
really owe their development to grasses.

Man’s first attempts to control his fate, to provide for
future need instead of remaining the victim of droughts
or other untoward circumstances, which were the begin-
nings of civilization, must have been on grasslands where

[203]

GRASS

the young calves, lambs, and kids he caught and tamed
could find forage. It was on grasslands, too, that primi-
tive man, after he had reached the food-producing as dis-
tinguished from the food-gathering stage, developed most
rapidly. The earliest known records of human culture
are found in the Nile Valley and in southwestern Asia,
open country of scanty rainfall. It is perhaps significant
that the most primitive tribes of living men, the pygmies
of Africa, New Guinea, and the Philippines, are found
only in forested regions. Sheltered in the depths of the
forest they have led their timid lives, so near the verge of
starvation that they are relatively few and remain in the
Stone Age to this day.

It was while the ice of the fourth Glacial Period covered
most of Europe, some hundred thousand to five hundred
thousand years ago, according to Breasted, that the
earliest Nile dwellers slowly changed from hunters to
breeders of flocks and tillers of the soil. Wheat, with ages
of selective cultivation behind it, has been found in some
of the oldest known graves in the world, in the Nile Valley.
The stomachs of bodies from these early cemeteries con-
tain husks of barley and of a kind of millet (Echinochloa
colonum) no longer cultivated. In the Nile Valley the
cultivation of grain seems to have preceded the grazing
industry, but breeding of donkeys, sheep, and cattle was
well established by 3500 B.c.

In Europe the hunters of the Old Stone Age advanced
but slowly until the final retreat of the glaciers some seven
to ten thousand years ago. But the domesticated or half
domesticated animals of the Nile Valley and the eastern
shores of the Mediterranean somehow found their way into
Europe, following steppes and valleys until in time they
reached the grassy Swiss uplands, where they were again
domesticated by the Swiss lake dwellers.

For thousands of years the women of those early ages
had gathered the seeds of wild grasses, crushed them be-
tween stones, and made cakes of them. At an early

[ 204 ]

THE BASIS OF CIVILIZATION

period barley and wheat somehow reached these lake-
dwellers, for these grains have been found in the remains
of Swiss lake villages. Men as well as cattle must have
wandered from the East, each generation going further
west and carrying seed grain with them. With grain and
cattle the Europeans of the Late Stone Age were able to
advance rapidly from a life of hunting to one of settled
communities of cultivators and cattle breeders. As in
Egypt the two types of culture, growing of grain and cattle
raising, both based on grasses, proceeded together, the
prototype of modern farming.

In western Asia the hunter developed primarily into a
cattle breeder, depending on the wild grasslands for
forage, ever wandering in search of fresh pasture. When
Abram and his family set out from Ur, between the
Euphrates and the desert of Arabia, “to go into the land
of Canaan,” he was a herdsman, doubtless seeking new
grazing lands. He followed up the valley of the Euphrates,
far to the north, instead of striking across the desert to
Canaan, and stopped at Haran (later called Charan) in
upper Mesopotamia, a region of good pasture land. Later
Abram wandered southward in the country bordering the
Mediterranean, stopping where he found water and pas-
turage, until, when “there was a famine in the land,” he
drove his ‘‘sheep and oxen and he-asses and she-asses and
camels” down into Egypt. In that fertile land Abram
became “very rich,” that is, his stock increased, until,
on returning to Canaan with his nephew Lot, they had
such vast droves of animals “the land was not able to
bear them.” And “there was strife between the herdsmen
of Abram’s cattle and the herdsmen of Lot’s cattle,” even
as there was between the cattlemen of our Western States
in the seventies and eighties of the last century. Later
there was trouble with Abimelech over a well and more
strife between herdsmen, and so the story of the patri-
archs unfolds, always against a background of seeking
grazing land and trying to holdit. Famine came in Isaac’s

[205 |

GRASS

day and he sowed a field “‘and received in the same year
an hundredfold.”” This is the first mention in the Bible of
sowing, but what Isaac sowed we do not know. The first
mention of grain is in the passage where Isaac, blessing
Jacob by mistake for Esau, says, “God give thee...
plenty of corn.” This corn must have been wheat or
barley, both of which were cultivated in Egypt and ad-
joining regions centuries earlier.

The Indo-Europeans, our own ancestors, were already
herdsmen when, some forty-five hundred years ago, they
began to spread from the great grassy steppes which lie
east and northeast of the Caspian Sea. Tribe after tribe
of these nomads wandered across Europe seeking pasture,
until they reached the westernmost land, the British
Isles. Besides cattle and sheep, these people had horses.
Among the Hebrews and other Semitic tribes donkeys
were used as beasts of burden and camels for riding. The
early European tribes were horsemen, the great-great-
grandfathers of our cowboys. As these tribes found
promising land—the valley of the Danube, the plains of
Hungary or Lombardy, the valley of the Rhone—they
settled down, cultivating wheat and barley as well as
raising livestock, just as American pioneers took up home-
steads in the West. Middle and western Europe, being a
land of mixed forest and relatively small stretches of open
grassland, encouraged this settled life of farming and
progressive civilization. The great grasslands to the
north of the Black Sea and stretching far into Asia re-
mained the home of nomads, who depended on wild
pasture. As the tribes and their flocks increased they
became ever more warlike, fighting with one another, and
periodically—when there was a drought, probably, or
when the grasslands were depleted by long overgrazing—
moving out in vast hordes, overwhelming towns and agri-
cultural settlements. The Scythians before the Christian
era, and the Huns, Tatars, and Mongols, who later over-
ran Europe, were such swarming nomads. Much of his-

[ 206 |

THE BASIS OF (CIVILIZATION

tory is but the record of invasions of peoples seeking fresh
grasslands.

Grasses were the innocent cause of trade wars, also, for
caravans of camels or horses had to follow grasslands;
and these trade routes were fought for, as sea routes and
railways have been fought for in modern times.

GRASSES AND OLD Wor.LD CIVILIZATION

Although grazing was an advance over hunting it did not
forward civilization as did the cultivation of grain, which
compelled a settled abode. At the dawn of history the be-
ginning of such cultivation was so far in the past that
it had become a myth. In Egypt wheat was held to be
the gift of Isis, in Greece, of Ceres. Our breakfast
“cereals” commemorate the Greek myth to this day.
From Egypt and adjoining Asia, the cradle of a civiliza-
tion based on the cultivation and grazing of grasses, this
culture slowly spread in all directions, reaching from
China to the British Isles and down through Abyssinia to
the tribes of East Africa, a culture built up on the economic
foundation of grain fields and herds.

None of the cultivated races of wheat are known in the
wild state. A wild form of emmer (Triticum dicoccum) was
discovered in 1906 on Mount Hermon, in Palestine, and
later in Moab, by Aaron Aaronsohn, and called Triticum
dicoccoides by the German botanist, Koernicke. In 1g10
it was found again in western Persia, in the Zagros
Mountains. Itseems fairly certain that this is the ancestor
of cultivated wheat. In emmer and in its wild variety,
the axis of the head breaks up, the grain remaining in-
closed in the chaff. In cultivated wheat (Fig. 37) the axis
does not break up and the grain can readily be freed from
the chaff. This character must have been developed and
fixed by selection, yet so long ago was it accomplished
that the wheat found in the earliest known graves is free
from chaff. Breasted states that the stomachs of mum-
mies in these graves contain the chaff of barley, which,

[ 207 |

GRASS

Fic. 37. Heads of grasses. 1, four-rowed barley; 2, rice; 3,
cultivated wheat; 4, rye; 5, oats

[ 208 |

THE BASIS OF CIVILIZATION

being difficult to separate from the grain, was present in
the bread. The chaff of wheat is not found in the stom-
achs, because it was readily removed from the grain.

Tales have been told of the germination of wheat found
in Egyptian graves, and it has been claimed that the pecu-
liar wheat with branched heads called ““mummy wheat”
was derived from such seed.. These statements are not
credited by scientists. It must have been an easy matter
for a guide or other person to replenish the wheat in
graves shown to travelers, and doubtless many a traveler
was willing to pay well for a few grains of wheat from an
ancient jar found in a grave with a mummy. But the
so-called mummy wheat has not been found in Egyptian
graves, and authorities agree that it did not exist in
antiquity. Pharaoh’s dream of seven ears of corn on one
stalk suggests that the branched heads of wheat may have
appeared as occasional sports since early times, though
it was only in modern times that this form of wheat was
fixed by selection and breeding. Certain varieties of
Poulard wheats produce branched heads, especially in
Alaska, as do some of our native wheat grasses, such as
Agropyron smithit.

Barley was also cultivated in the New Stone Age, for
it is found in Egyptian pottery jars dating from 4000 B.c.
and in the remains of Swiss lake villages. The barley of
antiquity was the six-rowed kind (Hordeum hexastichon)
less commonly cultivated today than the four-rowed
(Hordeum vulgare). The two-rowed (Hordeum distichon),
also cultivated today, is the only form known to grow
wild. The four-rowed barley appears to have been de-
rived less anciently from Hordeum spontaneum, now
growing wild from the Caucasus to Persia and Arabia.

Wheat reached China long before the Christian era, but
rice is the more widely cultivated grain in eastern Asia. Rice
was developed in the dim past, being cultivated before
3000 B.c. In an ancient Chinese ceremony five kinds of
seed were planted, rice by the emperor himself, the other

[ 209 |

GRASS

four by princes of his family. Of the five, esteemed as
the greatest gift to the race, four are grasses, rice, wheat,
sorghum, and millet. The fifth is a legume, soya or soy
bean. Rice was cultivated in India in very early times;
thence it spread to Babylon, and finally, about a thou-
sand years later, it reached Syria and Egypt. It also
spread south and east throughout the Malay Archipelago.
In the Philippines today as for ages past rice is culti-
vated on the terraced mountain sides, the terraces holding
the rains and preventing erosion. In this conservation of
soil Philippine culture is far in advance of our own waste-
ful methods, which have resulted in denuding vast areas
of fertile top soil. There are forms of rice growing wild in
southeastern Asia which probably represent the species
from which the cultivated rice (Oryza sativa) was de-
veloped.

Rye came into cultivation far later than wheat, barley,
and rice, probably about the beginning of the Christian
era. It seems to have originated in a region farther north,
somewhere in the Russian steppes of Europe or Asia.
Unlike the earlier-known grains, rye will run wild and
maintain itself under favorable conditions for a time.
For this reason it is difficult to determine whether plants
that have been found growing wild were really wild forms
or descendants of cultivated rye.

The common oat (4vena sativa) is generally believed to
have been derived from the wild oat (4vena fatua); the
Algerian oat from Avena sterilis, and a few other varieties
from Avena barbata, all three species native to the Medi-
terranean region. Oats were known to the ancient Greeks
as weeds in grain fields, but appear to have been culti-
vated in middle Europe during the Bronze Age.

Sorghum (Sorghum vulgare) in various forms has been
widely cultivated for ages; but, though long grown by
Egyptians, it has not been found in the early tombs. A
number of closely related species are native to east-central
Africa. Sorghum was probably derived from one of

[210]

THE BASIS OF CIVILIZATION

them, and introduced in prehistoric time into Egypt,
whence it spread to India and China. In warm countries
sorghum seeds so heavily that it is the staple food of
millions of people, especially in Africa. Sweet sorghum
(Sorghum saccharatum) also was probably derived from a
central African species. It appears to have reached
Egypt after the time of the Pharaohs and to have spread
to Arabia, India, and China, where it is the kao-liang, or
“great millet” of the Chinese. In the United States kafir,
milo, and durra, forms of sorghum, are grown for seed
and for forage. Broom-corn sorghum is grown for its
great branching heads from which our brooms are made.
Sweet or saccharine sorghum or sorgo is cultivated for the
sweet juice extracted from the stem, which, boiled down,
was the delicious sorghum molasses so commonly made
by farmers of the Middle West a generation ago.

Several other species of grasses have been cultivated
by primitive peoples for the seed, but are now largely re-
placed by wheat and other grains. Common millet
(Panicum miliaceum), a native of Asia, probably reached
Europe nearly as early as wheat and barley, for it is found
in remains of Swiss lake dwellings. It has become natural-
ized in many temperate regions, including the United
States. Italian or foxtail millet, with a multitude of
derived forms, such as Hungarian millet and German
millet, was also commonly cultivated in prehistoric times,
apparently spreading westward from China, and reaching
Switzerland in the Stone Age. Pearl millet (Pennisetum
glaucum), another African grass, 1s grown in Africa and in
tropical Asia for food. At maturity the smooth and
shining grain bursts through its chaff, the long cylindrical
spike being thick set with these “pearls.” Coracan
(Eleusine coracana), a native of India, teff (Eragrostis
abyssinica), and fundi (Digitaria exile), natives of Africa,
are also cultivated in tropical Asia and Africa but are
unimportant compared to the grains.

Besides the grains, whose seeds furnish the breadstuffs

bona |

GRASS

of the world, there is another grass which is the source of
an important food, sugar. Sugar cane (Saccharum
officinarum) is now cultivated in all tropical and sub-
tropical regions of sufficient rainfall (Fig. 38). Compared
with the grains its cultivation is relatively recent. Sugar
cane seems to have
originated in south-
eastern Asia (New
Guinea, according to
to Brandes) and was
grown in China a
century or so before
the Christian era, but
was not known to
Europe until the
Middle Ages, when
it was introduced by
the Arabs into Sicily
and the south of
Spain. The ancients
had to depend on
honey for their sweet-
ening; hence the ideal
land, flowing with
milk (having plenty
of grass, that 1s) and
honey. Sugar cane
in cultivation rarely
flowers and very
Fic. 38. Sugar cane rarely sets seed. Since
the rich store of sugar
in the stem would be used by the plant in the production
of seed, the species has been artificially selected for
sterility. Plant breeders occasionally succeed in securing
seedlings, but sugar cane is propagated by planting
joints of the cane, which root at the nodes and send up
new stalks.

f-272) |

YIOIYIITY Aq ydeisoioyg “SPpUPR|ST UBTITEME LET eyy ul auvo Ivsns jo Pel

ene

Ee ee

OF ALWId

THE BASIS OF CIVILIZATION

GRASSES AND AMERINDIAN CULTURE

The culture-nucleus, based on cultivation of grain and
grazing, spread from Egypt and adjacent Asia throughout
the Eastern Hemisphere, except Australia, which devel-_
oped no civilization of its own. In America a second center :
of civilization arose, based on the cultivation of maize,
which like that of wheat began so far back in antiquity
that its origin is veiled in myth. To the American Indian
maize was a gift of the gods. One of the legends is familiar
to us—the one which relates how Hiawatha prayed that
the lives of his people might not depend on hunting and
fishing. In answer to his prayer came Mondamin, with
whom Hiawatha wrestled mightily, whom he buried, and
from whose grave, carefully tended according to Mon-
damin’s instructions, sprang maize, a never failing food
for the people. While Eurasia had wheat, barley, rice, and
the other grains America had but one. When the white man
arrived maize was cultivated from Central America south
to Peru and north to Quebec. The Inca, Maya, Aztec,
and Pueblo civilizations were based upon it, and it was
cultivated by the North American Indians over much of
what is now the United States. The hungry Pilgrim
Fathers, we are told, found a buried hoard of Indian corn
during their first terrible winter in the New World and
thankfully stole it. But for this lucky find there would
probably be fewer Mayflower descendants than there are
today. The Indians taught the Pilgrims how to plant
maize, or corn as it was called by the English settlers,
fertilizing it by burying two fish in each hill.

Maize (Fig. 39) has never been found growing wild, and
it 1s singularly unadapted to maintaining itself without
cultivation. No species growing wild is at all similar to
maize. There are wild species related to each of the Old
World grains, from which the cultivated form has probably
arisen; but maize (Zea mays) is the only known species
in its genus. The genus most nearly related to it is

ans)

GRASS

Euchlaena, to which belongs teosinte, a native of Mexico,
occasionally cultivated for forage.

Collins, who has made careful studies of maize and its

crosses and also of teosinte, is of the opinion that maize

originated as a hybrid be-

tween teosinte and an un-

known and extinct species

N\'/ resembling pod corn.
YG Maize is the most highly

specialized grass in the world;
and it was the American
Indian who, by artificial
selection through thousands
of years before the coming
of the white man, produced
this marvel of plant-breeding.

In the Old World the
primitive agriculturist had
domestic animals. The
American Indian cultivated
grain but had no cattle.
The American bison, or so-
called buffalo, is distantly
related to the ancestors of

. domestic cattle, and in the
;

mountains were wild sheep

ys and goats; but these Ameri-

CAT Wm can animals for'some reason

Fic. 39. Maize or Indian were never domesticated. In
corn South America the llama and

alpaca were domesticated as
beasts of burden, greatly inferior to the horse or donkey,
and as sources of wool, but nowhere did the Indians have
milk cattle. Though the horse originated in America, it
became extinct on this continent before or during the
Glacial Epoch and was unknown to the Indians until
introduced by the Spaniards.

[ 214]

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W ALV Id

yoooyoaipy Aq ydessojoyg “S}uaWIASIZOApe Iv [eM 943 UO sprederd ay, *ajqe3adaa v sev pasn SI UI9}S 94} Jo
qed JMO] aL “suryuryy fo sje ay apisqno ysnf wes ev Sursapsoq (v170 fv) viuvz17) dol UBIPUT asauTYy>

cy ALV Id

THE BASIS OF CIVILIZATION

The Indians of the Great Lakes had besides maize
another grain in the aquatic grass called wild rice, or
Indian rice (Zizania aquatica). Down to our own day the
Indians have gathered the wild rice, the women going
about in canoes and tying together the heads of as many
of the plants as could be gathered in the arms. These tied
heads were left to ripen, when the women returned and,
holding the tied heads over their canoes, beat out the
grain. From two to three thousand bushels a year have
been gathered in this way. Today Indian rice is an ex-
pensive dainty, served with game on the table of the
epicure. In China the young shoots of a perennial
species of Zizania are used as a potherb.

All the grains, to which man owes his civilization, are
annual grasses, that is, the plant bears one crop of seed
and dies. Perennial plants live over the winter or the dry
season by means of underground parts that remain alive
but dormant. Such plants usually bear fewer seed of less
viability than do annuals, which must depend upon their
seed for survival. An annual that failed to bear good
seed would become extinct. Primitive man, or woman,
rather, gathering seeds of grasses to add to the food sup-
ply, naturally took those of annuals, which were larger
and more abundant. Annuals, being short-lived, produce
seed within a few months after planting, while perennials
seldom bear seed the first year. Naturally, then, it was
annuals that were chosen for cultivation.

[215]

CHAPTER II
GRASSES THE BASIS: OF WEALTH

So long as man depended on the chase there was danger of
famine. By domesticating animals he greatly lessened
this danger; but in a prolonged drought the grass would
fail and the cattle perish, as has so often happened in our
own Southwest. The cultivation of grain afforded a
much more certain insurance against famine, for the grain
could be stored from one harvest to another or for many
years. The shrewd Joseph stored surplus grain for seven
fat years; and then in the seven lean years that followed
reduced the Egyptians to serfs by selling them back the
grain they had raised and he had stored.

Grasses are the greatest single source of wealth in the
world; for bread is in truth the staff of life, even if man
does not live by bread alone. The prominent place the
grass family occupies in the economic life of the world
may be shown by a few statistics from the census reports
on the value of farm crops in the United States.

The total value of farm crops for 1927 was more than
nine billion dollars. Of this more than two billion, or
nearly one-fourth of the whole, is credited to maize (corn).
The next most valuable single crop is not a grass, but
cotton, worth, fiber and seed, one and a half billion
dollars. The third most valuable crop is grass, in the
form of hay, the wild and tame together being valued at
one and a third billions. Wheat, barley, oats, and rye
together are valued at one and two-thirds billions. In
round numbers the grass family, not even including rice,
sugar cane, millets, crops of grass seed, and other lesser

[ 216 ]

THE BASIS OF WEALTH

items, accounts for five billion dollars of the total of nine
billions, that is, more than all other crops, cotton, tobacco,
fruits, and the rest, taken together.

Our agricultural statistics do not give the value of
pasture, but in the aggregate it must reach an enormous
figure. Every farm has its pasture land and vast areas
in our Western States furnish forage, largely of grasses, to
grazing animals. A large part of the value of dairy prod-
ucts and of beef and mutton must be credited to grasses.
The proportional value of the grass family in agriculture
is about the same throughout the world, rice and sugar
cane being the most important in the tropical regions.
The chief food plants of the world are the grains, legumes
(beans, peas, lentils), potatoes, bananas and plantains,
cassava, yams, breadfruit, taro, and the sago palm. Ex-
cept among some primitive peoples the grains furnish the
principal food, the others being supplementary.

Besides our daily bread, wheat bread or corn pone,
knackbrod or bannocks, schwarzbrod or macaroni, rice
or cakes of millet or sorghum, the grains furnish other
important food products. Maize, the one native American
grain, is a host in itself, giving us delicious sweet corn,
pop corn, corn flakes, cornstarch, hominy, glucose, corn
syrup, and a palatable oil besides. This oil, “Mazola,”
is obtained from the germ in the kernel of corn, a bushel
of corn yielding about a pound of oil. As a by-product
the germ yields a rubber substitute, the “red-rubber”
now in common use as erasers, rings for fruit j jars, sponges,
and spongy rubber soap dishes and bath mats. Dextrin
obtained from cornstarch has replaced gum arabic as
the basis of mucilage. According to Slosson “‘more than
a hundred different commercial products are now made
from corn, not counting cob pipes.” Cornstalks, formerly
a waste product of huge proportions, are now coming into
use as a source of cellulose and promise to be of especial
value in the production of paper and of wall board. A
corncob stone, called maizolith, has recently been de-

[217']

GRASS

veloped. It can be worked and polished and used for such
purposes as are now supplied by hard rubber and bakelite.
Corn is also a source of alcohol. As Slosson further says,
“This was, in fact, one of the earliest misuses to which
corn was put, and before the war put a stop to 1t 34,000,000
bushels went to the making of whiskey in the United States
every year, not counting the moonshiners’ output... .
The output of alcohol, denatured for industrial purposes,
is more than three times what it was before the war.”

Rye and barley are used extensively in making fer-
mented and distilled beverages, and in the Orient a wine
is made from rice. Much of the commercial vinegar is
made from malt liquor, the alcohol being converted into
acetic acid (the acid of vinegar) by means of ferments.

The juice extracted from the stems of sugar cane is
concentrated until the sugar (sucrose) crystallizes and can
be separated from the molasses. In earlier days the sugar
was only partly extracted from the juice and the molasses,
still rich in sugar, was an important by-product. Much
of the molasses was used in the production of rum. With
modern methods the separation of sugar is so nearly com-
plete that the residue has little value. The bagasse, or
crushed cane from which the juice has been extracted, is
now being used in the manufacture of wall boards.

RANGE AND PASTURE

Besides supplying us with our daily bread, the grasses,
by providing a large part of the forage of grazing animals,
indirectly supply us with dairy products, beef and mutton,
wool, leather, and horsepower. And, since hogs and
poultry are fed largely on maize, ham and eggs are also
secondary products of the grasses.

The range is the modern equivalent of the grasslands of
our remote nomad ancestors. It is unfenced public land
upon which the cattle and sheep of several stockmen graze
in common, the cattle being separated at a yearly round-
up according to their brands, the calves being branded

[| 218 |

THE BASIS OF WEALTH

with the mark borne by the cows they claim as mothers.
Our Western States were once immensely rich in good
range land, but the best of the land has now been settled
and brought under cultivation. But, even so, the acreage
upon which livestock is grazed exceeds that under culti-
vation. The figures for 1920
were 293,794,000 acres cul- sity
tivated and 350,000,000 acres Ye
used for grazing. | wp
The range lands lie almost
entirely west of the tooth
meridian and comprise the
vast semiarid region, with an
average annual rainfall of less
thantwentyinches. Thisland, a
covered with the hardy and \
nutritious buffalo grass and \
erama grasses (Fig. 40), the \
wheat grasses, bromes, por-
cupine grasses and numerous aN
other native species, affords ANAS
excellent grazing. Dry farm- NK
ing is feasible on part of it
but stock grazing appears to
be the most economical use
to which it can be put. Until
.the end of the last century
the Federal Government al-
lowed stockmen uncontrolled
use of the public domain. As Fic. 40. Tuft of grama
a result rolling hills knee-deep — grass, an important
in grass were reduced to bare range grass
knobs, deeply gullied, their
fine soil eroded and blown over the land in blinding
dust storms; and vast natural pastures of grama grass
were despoiled of their palatable and valuable forage
and given over to worthless plants or left denuded and

[ 219]

Eg ge
$ Z Z z= e &
amy SZZ

L——==
SENS

GRASS

subject to erosion. When more stock than the land can
support are grazed upon it, the hungry animals not only
devour the good forage so completely that no plants are
allowed to seed and so replenish the range, but also, in
extreme cases, paw the plants and eat them to the very
roots. The unpalatable plants and those covered with
spines are avoided by the cattle, hence these worthless
plants bear seed and replace the good forage. When we
read of the wars of the Hebrews and the neighboring
tribes in the light of the history of our western range
lands we are impressed with the fact that overgrazing
changed the Promised Land of plenty to a land of want.
“He turneth a fruitful land into barrenness for the wicked-
ness of them that dwell therein,” says the Psalmist. Sub-
stitute ignorance for wickedness and it is literally true.

One of the great achievements of the United States
Department of Agriculture has been the study of grazing
problems, and the working out of a system of licensed use
of grazing lands. Much of the public range is now under
the control of the Forest Service. Permits are issued to
stockmen which limit the stock to the number which the
range can bear without injury, and are so timed as to per-
mit the plants to set seed, thus restocking the depleted
range. The wars and invasions of the ancient nomads
were due to the fact that they were ignorant of range
management, as, indeed, are many peoples today. Great
areas of the once luxuriant campos of parts of Brazil are
now denuded and badly eroded from long-continued
overgrazing.

Pasture is grassland brought under control. In former
times villages had pasture land in common, where the
cattle of the villagers grazed under the care of a few chil-
dren. The “commons” or “greens” of English villages
and our own Boston Common were originally such public
pastures. Now that townspeople no longer keep cows
our “commons” have become parks, and pastures are parts
of privately owned farms. Until very recently improve-

[220 |

THE BASIS‘OF WEALTH

ment of pastures has not kept pace with other improve-
ments in farm management. ‘Only the fact that grass will
stand an almost incredible amount of abuse has pre-
vented its utter destruction. Relegated to land too rough
to till, neglected by the farmer, abused by the grazier,

~
\ SSS NB)
oh NIWA

Fic. 41. Kentucky blue grass

permanent pastures still furnish one-third the feed con-
sumed by domestic animals.” as a writer in the Rura/
New Yorker truly says.

Blue grass or Kentucky blue grass (Fig. 41) is the stand-
ard pasture grass for the humid region of the United

[ 2ar |

GRASS

States, while Bermuda grass (Fig. 42) is the standard
pasture grass for the Southern States. Both these grasses
are sod formers, with tough rhizomes or rootstocks form-
ing a close turf that withstands grazing and the trampling
of hoofs. Both were early introduced from Europe, the

Fic. 42. Bermuda grass, showing habit of growth

blue grass from north Europe, and Bermuda from the
Mediterranean (Kentucky and Bermuda both being
misnomers).

In regions of snowbound winters pastures provide forage.
for but part of the year, and additional feed must be stored
for winter. Such feed in the form of hay is cut from
meadows, cultivated or wild. In the United States the
hay from wild grass, once of major importance, is de-
creasing rapidly as more and more land is brought under
cultivation.

Until the last century or so forage grasses were not cul-
tivated in the sense of sowing seed of a single species. The
first forage grass to be cultivated was English rye grass
(Lolium perenne), which came into use in England about
250 years ago. Other grasses came into use later, until
at the present time about fifty species are cultivated for

[2297]

THE BASIS OF WEALTH

meadow or pasture, several of them to but a limited extent.
Although most of these species are cultivated in the
United States only a few are of prime importance.
Timothy (Fig. 43, left) is the foremost meadow grass
for the Northeastern States and for the humid regions of

\ | WZ
Wi : pe
\ | Vv WALA
i VEZ
\ v iy ie _

Fic. 43. Heads of timothy (left) and orchard grass (right)

the Northwest. It is the standard hay upon the market,
that by which other hay is measured. Timothy was one of
the earliest grasses to be cultivated for hay in this coun-
try and at once became dominant. It is not more nutritious
than many other grasses, but its cheap and reliable seed
recommend it to growers. The timothy seed is borne in a
compact head and does not shatter easily when gathered.
The whole crop ripens at approximately the same time
and the heads are borne at a fairly uniform height, which
make the seed crop easy to harvest. These qualities

eae

GRASS

combine to produce low-priced seed. The hay itself is
easily grown and harvested, it cures well and is palatable
and nutritious.

A few other grasses are important in certain areas, but
none compare with blue grass and Bermuda for pasture
and with timothy for hay. Redtop, orchard grass, and
meadow fescue are grown for hay and pasture in the
humid regions. Johnson grass, a perennial relative of the
sorghums, is an important hay grass in the Southern States,
but, because of its very aggressive rhizomes, it is an ex-
ceedingly troublesome weed in cultivated soil. Brome
grass, because it is drought-resistant, has found favor in
the semiarid region from Kansas to Minnesota and eastern
Washington. On the Pacific Coast, wheat and oats,
grown as a winter crop, are cut for hay. In California this
grain hay is valued in the thirteenth census report at
nearly twice that made from alfalfa.

Of relatively minor importance are rye grass, and tall oat
grass, grown in the Northern States, and paspalum, in the
Gulf States. The latter is a valuable forage grass in
Hawai and Guam, especially for dairy cattle.

Guinea grass and Para grass are valuable in the tropical
countries south of us, but can be grown in the United
States only in southern Florida and southern Texas.

Forage is preserved not only as hay, but also as silage,
which is prepared by packing the freshly cut forage, mostly
maize stalks, leaves, and ears, in an air-tight receptacle
called a silo. The mass ferments a little, becoming a mild
forage sauerkraut, readily eaten by cattle.

In tropical countries, where the climate is not suited to
haymaking, soiling, that is, the feeding of freshly cut forage
to animals in inclosures, 1s commonly practised. A
donkey trudging toward town almost hidden beneath a
load of green grass is a frequent sight in the American
Tropics. Soiling 1s also adapted to intensive farming,
especially dairying, because large leafy grasses and legumes
that would not endure trampling by stock can be grown,

[ 224 ]

THE BASIS OF WEALTH

which yield a larger amount of feed per acre than does
pasture. But the amount of labor involved in soiling
makes its cost prohibitive in most parts of this country.
Teosinte, the wild grass most nearly related to maize,
is grown for soiling in parts of Louisiana, where it yields
an enormous amount of forage.

All these cultivated grasses are foreigners, mostly
natives of Europe. Paspalum and teosinte come from the
American Tropics. Only one of the fifty species culti-
vated in the United States is a native of this country.
This is slender wheat grass (4gropyron tenerum), which
is cultivated for hay to a very limited extent in the
Northwestern States. Our prairies, plains, and upland
meadows support numerous native species that are
palatable and nutritious, but none of them has been
found adapted to cultivation. This is due principally to
the high cost of their seed. The grasses which best with-
stand grazing are sod formers. Perennials as a whole
produce fewer and less viable seed than do annuals, and sod-
forming grasses particularly, spreading vegetatively, do
not produce large seed crops. Timothy, as stated before,
is exceptional and is the preeminent meadow grass.

The United States Department of Agriculture and our
State experiment stations have been for forty years test-
ing grasses from all parts of the world, but the results are
surprisingly small. Brome grass or Hungarian brome
(Bromus inermis) 1s a comparatively recent introduction
from Europe, where it had already come into cultivation.
Rhodes grass (Chloris gayana), from Africa, gives promise
for the irrigated regions of the Southwest.

The desire for miracles in grasses as in other things leads
dealers occasionally to offer “‘mortgage-raisers” and the
like, which turn out to be no better nor as good as grasses
already in use. “Billion-dollar grass,” widely advertised
some years ago, is a variety of our common barnyard
grass (Echinochloa crusgalli). The rich well-watered soil
required for its growth would produce a far more valuable

(haa, |

GRASS

crop of timothy. A so-called “Peruvian winter grass”’ is
being sold at an enormous price, entirely out of propor-
tion toits value. It is a variety of Phalaris tuberosa having
rhizomes, was described from Australia, where it was
introduced from Europe, and has been experimentally
grown in California.

The grasses now grown in the humid region and 1n irri-
gated areas in this country are well suited to them. It is
the ranchmen of the Southwest who are hoping for some
grass that will make two blades grow where none grow
now on their arid and semiarid acres, especially those
depleted by overgrazing; for stockmen have impoverished
their own as well as public lands by this practice. In a
dry year in western Texas or in New Mexico one may
hear a ranchman, holding on to his too numerous and
starving cattle in the hope of rain, bitterly complain: “It’s
funny the Department of Agriculture can’t find some grass
that will grow on this land.” The fact is that the best
possible grass for that land did grow there until destroyed
by overstocking. No grass, and certainly no other kind
of forage—for grasses are the most long-suffering of all
forage plants—can grow where it is grazed to its roots.

Lanp BuILDING

Along our North Atlantic Coast and at the south end
of Lake Michigan are great hills of sand, piled up by wind
and wave. These sand dunes, unless held by vegetation,
travel inland, a thin layer of the upper, driest sand blowing
up the windward side and sliding down the lee side, the
dune advancing from a few inches to a few feet in a
year. The great dune at Cape Henry, Virginia, is thus
moving and is burying a cypress swamp. One may
walk down the lee side of the dune through the tops of cy-
press trees sticking out of the sand and come into the still
unburied swamp. Where the land back of a dune is
valuable, as on the Massachusetts coast and at the head
of Lake Michigan, the advancing dunes cause great loss.

| 226 |

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as " Le Vo lg <=

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THE, Basis OF WEALTH

Several species of grasses having strong rhizomes flourish
on these wind-swept sands and serve to bind them. The
principal species is beach grass or marram-grass (4mmo-
phila breviligulata) (Fig. 44). When unusually severe win-
ter storms or destruction by man make a break in the pro-
tecting zone of this
grass a “‘blow-out”’
is likely to develop,
which rapidly opens
great gaps in the
barren dunes, per-
mitting the sand to
sweep inland, cover-
ing towns and farm
lands. The attempt
of real-estate men
to “‘clear away the
sand hills” in order
to develop summer
resorts on the coast
has had disastrous
effects in places. It
would be as safe to
clear away the dikes
on the coast of

Wolaad: Hae an. Beach grass, showing habit
of growth which makes it an excellent
In Denmark, Hol- sand binder

land, and along the

Baltic, barrier dunes are under the care of the government.
Areas of bare sand are planted with beach grass (d4m-
mophila arenaria, closely allied to our own species) and
accidental breaks are replanted.

All marsh grasses are slowly building up meadow land.
On mud flats and tidal estuaries such as those in the Gulf
of St. Lawrence, Chesapeake Bay, and San Francisco
Bay, species of cord grass (Spartina alterniflora, 8. cyno-
suroides, S. foliosa, S. patens, and others) are building up

[227]

GRASS

dry land. These grasses thrive in the soft mud sub-
merged at high tide, their stout rhizomes forming a dense
firm network ever pushing seaward. The coarse grass
impedes the oncoming waves, protecting the shore while
causing the water to drop its burden of silt, thus building
up the floor until it becomes, first, marsh meadow, then
dry land, when the Spartina dies out, leaving the land
ready for the plow. This land building by Spartina has
been going on along our coasts for ages, and it is going on
today on a gigantic scale along the English Channel and
the North Sea. The traveler on a ship entering South-
ampton today will see vast green meadows of Spartina
stretching into the sea. Fifty years ago these were only
bare mud flats. Spartina Townsendii, called “rice grass”
by the English, a species closely related to S. alterniflora
of the North American coasts, was first observed on the
Southampton salt marshes in 1870. It now occupies the
tidal flats for a stretch of one hundred and fifty miles
along the south coast of England. “These bottomless
muds, though they stood empty of vegetation...
probably for thousands of years, found no plant capable
of solving the problems of invasion and establishment
till Spartina Townsendii came and made light of the task,”
says Prof. F. W. Oliver. On the French coast of the
English Channel Spartina Townsendii now occupies the
tidal flats along the Baie de la Seine, and has appeared
near the Strait of Dover. A few years ago this grass was
planted on the tidal flats on the east coast of England to
protect the sea walls of Essex.

Cuttings of this grass have been sent to Ireland, the
Netherlands, and Germany for reclamation work, which
has proved especially successful in the Netherlands.
(Plate 44.) In 1924 the grass was planted on the tidal
mud of the Sloe, opening into the West Scheldt, and later
along the East Scheldt also. The plants were set outside
the dikes in rows at right angles to them. The force of
the tide was thus divided and conquered, where crosswise

228:

PLATE 45

me fl Y q

cS
xe i?

: ES AG ue Lake
a2 Cs ene 7 “ = ° | Ay >
RNG SE Aes Pais: ; : Cte Bae

A clump of bamboo in China. Photograph by Hitchcock

PLATE 46

Uses of grasses in China

Upper: A lime kiln on the island of Hainan, China, the wall of which is
bamboo. Lower: Joss sticks of split bamboo drying in the sun, Canton.
Photographs by Hitchcock

THE BASIS OF WEALTH

plantings might have been uprooted and washed away.
The tufts are spreading and filling in the spaces between
them, soon to form a solid meadow and later arable
land, thus within five years accomplishing the recla-
mation of miles of land which, left to nature, would take
twenty years or more.

OrHER USEs or GRASSES

The bamboos (Plate 45), the largest of the grasses, are
of vast importance in the regions in which they grow,
especially from Japan to India and Malaysia. The larger
kinds reach a height of a hundred feet and are six to
ten or twelve inches thick below, tapering to the summit.
The culms or stems are very strong and are used in build-
ing houses and bridges. When the stems are split, flat-
tened out, and the partitions at the joints removed they
make very durable boards, a foot or more wide, for floors
and walls. Rafts and floats are made of the hollow stems
closed at the joints by air-tight partitions. With the
partitions removed bamboo stems furnish water pipes or
conduits. Sections of the stem closed at one end by the
partition form convenient vessels for holding water.
Much of the furniture, and many of the utensils and
implements used by the Malays are made wholly or in
part of bamboo. Slender bamboo stems are familiar
to us in the form of fishing rods and walking canes. Shoots
of Bambusa Beecheyana and other species of bamboo are
a choice vegetable in the Orient and an expensive dainty in
this country.

Grasses are an important source of fiber for paper
making and cordage. England annually imports more
than two hundred thousand tons of esparto grass (Lygeum
spartum and Stipa tenacissima) from Spain and North
Africa for paper making. Species of Spartina are used for
cordage and the roots of Epicampes macroura, a Mexican
grass, make the stout “fiber” scrubbing brushes now on
the market. Brooms are made of the seed heads of

[ 229 |

GRASS

“broom corn,” a kind of sorghum. Rice straw is used for
matting and oat straw for straw hats. Leghorn hats are
made of a kind of wheat straw cut young and bleached.

Tons of essential oils used in perfumeries are extracted
annually from Asiatic grasses related to our broom sedge.
A few of them are cultivated throughout the Tropics.
One of them, citronella grass, is the source of the “fly
dope” used by fishermen and campers as less unbearable
than mosquitoes and black flies.

The resourceful pioneers who first settled the treeless
regions of our Western States made grasses take the place
of timber, building their houses of blocks of sod piled
up into thick walls, which defied the blizzards of winter
and the heat of summer. The sod house was to the
pioneer of the plains what the log cabin was to the pioneer
in wooded country. Today in the Andes the sheep herder
builds his hut of sod and roofs it with ichu grass (Plate 47).
The poor peasant in China uses grass for fuel to cook his
meager dinner.

InyjuR1ous GRASSES

The grass family, like many other fine families, in-
cludes a few vicious members. There are the weedy crab
grass, couch grass, and the like, that cost the gardener and
cultivator much labor, but they are troublesome only in
being too hardy, and in coming where they are not
wanted. The villains of the grass family are those that
carry spears and daggers and use them without mercy
(Figs. 45 and 46). Our native ruffians are bad enough, but
a group of assassins from the Mediterranean join in their
nefarious work. The native sand burs (species of Cenchrus)
with their little balls covered with spines as sharp as
needles, are troublesome to man and beast. The ripe
spikelets of Heteropogon contortus, a relative of the broom
sedges, have sharp barbed spears at one end and a stout
twisted appendage at the other. The spear catches in
the wool of passing sheep and the appendage untwists

[ 230 ]

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ssvi3 nyoI Jo Joos ay], ‘Pos Jo ase sypeM ayy *(3997 Ooo'f1) nsag ‘sapuy YysrYy ayy ul siny siapsay daays

Lv ALWId

THE BASIS OF WEALTH

Fic. 45. Villainous native grasses. I, 2, 5, needle grasses; 3,
needle grama; 4, Scleropogon; 6, porcupine grass; 7, 8, sandburs;
9, Heteropogon

Moxie

GRASS

and twists, in dew and sunshine, thus driving the barbed
point through the wool into the skin. Some of the in-
vaders from the Mediterranean region are near akin to the
grains which have so blessed mankind. The barley grasses
(wild species of Hordeum) have bristly spikes which break
up at maturity, each joint having a sharp barbed point
and six or seven rough bristles. The points work into
the mouth parts, nostrils, and eyes of grazing animals,
causing painful sores and sometimes death. Our native
squirrel-tail barley is almost as vicious as its European
relatives. Sitanion, a related but wholly American genus,
has heads which break up as do those of barley grasses and
which are equally injurious to stock. An exceedingly
unwelcome invader from southern Europe has appeared
in recent years in California, Colorado, and Oklahoma.
This is goat grass (Aegilops triuncialis), a relative of
wheat. Its murderous tactics are like those of the barley
grasses, but its Joints are stouter and its barbs are stronger
and constitute a really horrible instrument of torture, the
barbs making it impossible for an animal to get rid of it
when once taken into the mouth. A few brome grasses,
also from the Mediterranean region, have large spikelets,
the florets of which disjoint with a sharp barbed point at
oneend and a long bristle at the other, and inflict injury
in the same way as do the barley grasses. The worst of
these, Bromus rigidus, the California stockmen feelingly
call “‘ripgut grass.”

DECORATIVE VALUE OF GRASSES

When through the cultivation of grasses man 1s freed
from the fear of famine, his love of beauty seeks satisfac-
tion and again grasses in large part meet his need. Our
European ancestors came from humid country where
meadows are a natural part of the landscape. The village
common was a meadow, mowed and fertilized by cows or
sheep. When the cattle were stabled for the night the
village green became the playground for the people, the

lees

THE BASIS OF WEALTH

Fic. 46. Villainous introduced grasses. 1, soft chess; 2, ripgut;
3, goat grass; 4, wall barley

[ 233 |

GRASS

place for dances and festivities. The love of greensward
is born in us. Most of our parks have more grassland
than woods or flower gardens. As soon as an American
acquires a home of his own with a bit of ground around it
he attempts to make a lawn. Probably nowhere in the
world is so much effort expended in lawn making as in the
United States. The results are often pathetically indif-
ferent, partly through ignorance, but largely because,
- except in the cool humid regions of the Northern States,
our country has not the moist climate of our ancestral
Europe. Our dry summers with scorching heat favor the
plains type of grasses, coarse and bunchy, not the fine soft
turfy grasses which make velvety lawns. A tale is told of
an American landscape gardener visiting England who
begged an English gardener to tell him the secret of the
wonderful lawns in that country, and giving him good
American money for the information. The English
gardener replied, “Well, you plow it up and fertilize it
and sow grass, then in a few years you plow that under,
and sow it again. After you have kept that up two or
three hundred years you'll have a good lawn.”

It takes knowledge and work and time to make a lawn,
especially in a region of hot dry summers. The home
gardener often makes conditions already unfavorable still
more so by terracing his ground with the sterile earth exca-
vated for his house, lifting the surface a foot or more
higher than natural above the water table, so that the
grass roots can not reach the moisture below. By copious
watering he induces the grass to spread its roots near the
surface; the scorching sun dries the top soil and the plants
suffer. Shrubbery and perennial borders are much easier
to establish and maintain, though some lawn is neces-
sary as a foreground in the picture that a well-planned
garden makes.

The chief lawn grasses for the humid temperate regions
are Kentucky blue grass (Poa pratensis) and certain species
of bent grasses (/4grostis), such as creeping bent, col-

[ 234 ]

PLATE 48

Pampas grass (Cortaderia selloana) in the Hawaiian Islands. Cultivated
for ornament. Photograph by Hitchcock

THE BASIS OF WEALTH

onial bent, velvet bent, and brown bent. Where these
grasses thrive, beautiful lawns may be established by pre-
paring the soil and planting good seed. ‘““The custom of
applying a layer of vegetation, part grass and part a
miscellaneous collection of weeds, to a soil consisting of
the refuse from building operations will never give satis-
factory results. Such a lawn is a permanent source of
regret and no amount of faithful watering can materially
improve it.” In the Southern States Bermuda grass
(Cynodon dactylon) is extensively used for lawns.

The growing popularity of golf, which serves to miti-
gate the strain of urban life, has created a demand for
good turf grasses. Golf, like our ancestors, came from
humid Europe, where grazed meadow land offered natural
golf grounds. Much time and money are being devoted
to golf greens, and many experiments are being carried
on in the hope of improving them. When the best
grasses for different regions have been found and the best
methods of treatment have been worked out, the home
gardener can appropriate the knowledge to the bettering
of his lawn.

A number of grasses are cultivated as ornamentals.
Great clumps of plume grass (Erianthus Ravennae), giant
reed (4rundo donax), pampas grass (Cortaderia Selloana,
Plate 48) and eulalia (Miscanthus sinensis) are often seen
in our parks and public squares. Eulalia, however, is an
ageressive weed, spreading rapidly, and its cultivation
should be discouraged. Fountain grass (Pennisetum
Ruppelii), with slender pale-pink panicles, is commonly
used, though not to the best advantage, as a border for
circular beds of cannas.

In warm countries the bamboos are planted in parks and
gardens. One of the most beautiful sights on earth is the
bamboo grove in the botanical garden at Rio de Janeiro.
Fven at Kew Gardens, near London, a charming bamboo
garden flourishes with hardy shrubby and dwarf species.

In this country we have a large number of beautiful

[235 |

GRASS

native grasses that deserve to be cultivated as ornamentals.
One of the loveliest is the broad-leaved uniola (Uniola
latifolia), which grows in low woods from Pennsylvania
to eastern Kansas and southward (Fig. 47). Though a
woodland grass it flourishes in open sunlight and takes

Fic. 47. Broadleaf Uniola

readily to domestication. The graceful clumps, with
stems three to four feet tall, broad-spreading leaves, and
drooping panicles of large very flat spikelets, are charm-
ing in a perennial border, or in shaded ground under tall
trees. A few stems with their graceful panicles in a slender
vase, or a greater number arranged in a standard in. a
flat bowl are very decorative in the house.

Any of the broad-leaved panic grasses (Panicum clan-
destinum, P. latifolium, P. Boscii or P. commutatum) pro-

[ 236 |

THE BASIS OF WEALTH

duce good foliage effects. In spring and early summer their
stems are simple, but by midsummer they begin to branch,
and by September they look like miniature shrubby
bamboos, quite Japanese in effect.

In the Rocky Mountain region and westward are sev-
eral melic grasses (Melica spectabilis, M. bulbosa, M. stricta
and others) with large spikelets of purple or bronze and
pale green, as lovely as any flower. Bottle-brush grass
(Hystrix patula), a woodland species of the eastern half
of the United States, is already cultivated to some extent,
but deserves wider use. A few of these grasses under a
spreading tree, with their slender gray stems, curving
leaves and swaying heads of horizontally spreading, long-
awned spikelets, suggest a dance of wood nymphs. These
and many other beautiful grasses of woods and prairie
are as ready to gladden our gardens, if we give them place,
as are wrens and bluebirds when we provide nesting boxes
and water for them.

ie)
ioe)
~I

CHAPTER Ti

THE PLACE OF GRASSES IN THE PEANE
WORLD

ALTHOUGH grasses have so important a place in the life of
mankind—indeed, “‘All flesh 7s grass’ —they are the least
noticed of flowering plants. They seem to be taken for
granted, like air and sunlight, and the general run of
people never give them a thought. Many do not even
know that grasses are flowering plants. Their flowers are
very small and are mostly hidden by the bracts of the
spikelet; but they are as truly flowers as are the gorgeous
blooms of the lilies, to which they are not so remotely
related. The flowers of grasses are borne on tiny special-
ized jointed branches, each flower inclosed in two bracts,
and with two empty bracts at the base of the branch.
This minute branch, with its bracts and flowers, is called
the spikelet (little spike). The typical arrangement 1s
really quite simple. In Figure 48, at the left, is a diagram
of a flowering branch with leaves and flowers arranged as
are the bracts and flowers of a grass spikelet; in the middle
is a diagram of a spikelet for comparison (the bracts
spread to show the flowers); and at the right is a spikelet
of brome grass. It will be seen that the spikelet is a
specialized leafy flowering branch, the branch jointed as
are the stems of all grasses, and the flowers two-ranked,
as are the leaves.

The essential organs of any flower are the stamens and
pistil. A stamen consists of an anther, which contains
the pollen, and the slender stalk which bears it; the pistil
consists of the ovary, which contains the ovules, and the

[ 238 ]

PLACE IN THE PLANT WORLD

stigma, which receives the pollen and is usually borne
on a relatively stout stalk. When the pollen (usually
of a different individual of the species) falls on the stigma
it germinates and sends its contents, in a minute tube
which pushes down through the style, to the ovules, fer-

Fic. 48. Left, diagram of a branch of an ordinary flowering

plant, with leaves and flowers arranged as are the bracts and flow-

ers of a grass spikelet; center, diagram of a grass spikelet with

the bracts spread to show the flowers; right, a spikelet of brome
; grass

tilizing them. The matured fertilized ovules are the seeds.
The foregoing is true of all flowering plants. In showy
flowers, like the lily or the rose, the essential organs are
surrounded by a brightly colored perianth or by petals.
These showy accessories protect the essential organs in
the bud and at blooming time attract insects, which
carry pollen from one flower to another, cross-fertilizing
them. The essential organs of the grass flower are pro-
tected by the bracts which inclose them (the lemma and

239°]

GRASS

palea). The abundant pollen is carried by the wind;
hence, having no need to attract insects, grass flowers have
only a rudimentary perianth, consisting of minute organs
called lodicules, which swell up at flowering time and
force open the lemma and palea, allowing the stamens
and the feathery stigmas to protrude. It is a common
observation that a stalk of maize standing by itself does
not usually bear a perfect ear of corn; sometimes it bears
only a cob with a few scattered kernels. This is because
the wind blows the pollen to one side and the silk receives
little. In a field of maize the pollen is effective except
on the windward border. Even if the flowers are perfect—
that is, the stamens and pistils in the same flower—as is
usual with grasses, there is some arrangement by which
the pollen of one flower is more likely to reach the pistil
of another flower than it is to fall directly on its own pistil.
For example, the anthers usually dangle on slender threads
below the stigmas, hence the pollen is blown away to
another flower.

There are many cases, however, in which the flowers
are self-pollinated. In some plants at least some of the
flowers are so hidden in the sheaths that they can not
open and cross-fertilization is impossible.

Grass spikelets are of many forms, but all are built on
the same general plan, and they are borne in heads of
various shapes and sizes. In wheat, barley, and rye the
spikelets are borne directly on the main axis, on opposite
sides, forming spikes. In oats, brome grasses and Ken-
tucky blue grass the spikelets, each on a little stem, are
borne on the branches of a panicle. In timothy the long
cylindric head is really a dense panicle, the spikelets
crowded on the numerous very short branches. In
Bermuda grass, Spartina, grama grasses, and the like, the
spikelets are borne on one side of the axis, forming a one-
sided spike. In broom sedges, sorghums, sugar cane, and
their relatives, the axis or branches of the inflorescence
break up, the joints remaining attached to the mature

[240 ]

PLACE IN THE PLANT WORLD

spikelet and aiding in the protection or dissemination of
the seed.

In maize, wild rice, buffalo grass, and some other
grasses, the flowers .are unisexual, the stamens and pistils
being borne in separate spikelets. In maize the staminate
spikelets are borne in a terminal panicle (the tassel), and
the pistillate spikelets in rows on a compound axis (the
cob), which is on a short leafy branch (the leaves being the
husks) i in the axil of a leaf. The “silk” of the ear of corn
consists of the numerous long styles with stigmas along
their sides. In wild rice the pistillate spikelets are borne
on the erect upper branches of a large panicle and the
staminate spikelets hang from the spreading lower
branches.

CLASSIFICATION OF GRASSES

There are such multitudes of different kinds of plants
(of grasses alone there are about six hundred genera) that
it is necessary to classify them in order to put our knowl-
edge of them in usable order. This classification is based
on genetic relationship, a sort of family tree. The plants
occupying the earth today are the survivors of millions of
generations. Countless forms have become extinct, some
of them leaving impressions in the rocks or in coal meas-
ures (fossils), but most of them leaving no record. The
relationship between some plants is obvious, the apple and
the pear, peas and beans, the walnuts and hickories, for
example. In these cases we assume that their common
ancestor is not so very far in the past, a mere hundred
thousand years or so. Somewhere in the buried past
were the intermediates, the connecting links, between the
most diverse of flowering plants. If the history of all
plants were known, the living species would be found con-
nected by lines of blood relationship running back millions
of years.

The unit of classification of plants is the species, which
is a group of individuals closely resembling each other and

[ 241 ]

GRASS

capable of freely interbreeding. Species that are evi-
dently related are grouped together, in a genus. The
black oak, white oak, burr oak, and shingle oak, are differ-
ent species of one genus, Quercus. Related genera are
grouped in families and families in classes. For con-
venience in recording our knowledge concerning plants
these genera and species are given Latin names. This
custom was adopted in the days when Latin was the
language of learning, when English, German, Swedish, or
French university professors alike gave their lectures in
Latin. It is continued today because, so far as the names
of plants go, Latin is still an infcraenionel language.
What we call barley, the Germans, Gerste, the French,
orge, in Latin is Hordeum vulgare, and plantsmen of all
countries use that name. The chief advantage of the
system of Latin names, however, is that these names indi-
cate the relationship of plants. All species of a genus have
the same generic name. Kentucky blue grass and all its
kind are Poa, Poa pratensis, P. trivialis, P. annua, P.
Sandbergii, and the like. The common names of these
—Kentucky blue grass, rough meadow-grass, spear-grass,
little bunch-grass, respectively—give no clue to their re-
lationship. Knowing Poa pratensis anyone familiar with
the Latin names of grasses, hearing of any grass named
Poa, has an idea of what it is like; it is something like Poa
pratensis.

Grasses, together with sedges, rushes, lilies, and other
families, belong in the class of monocotyledons, character-
ized by an embryo having a single seed leaf (cotyledon)
and by stems having woody fibers not in layers but dis-
tributed through them (as seen in the cornstalk). Anyone
will have observed that sprouting corn, rye, and other
grasses send up a single leaf first, whereas squash, radishes,
morning glories (which belong to the class of dicotyledons)

have a pair of opposite seed leaves. The grasses form a °

highly specialized family of about six hundred genera,
with a greater number of species than any other family,

[ 242 ]

——

i
ak

PLACE IN THE PLANT WORLD

except the orchids and composites (asters, dandelions,
thistles, and the like).

Grasses have been so successful in the struggle for ex-
istence that they have a wider range than any other
family, occupying all parts of the earth, and exceeding any
other in the number of individuals. They reach the
limits of vegetation, except for some lichens and algae,
in the polar regions and on mountain tops. They are
the dominant vegetation in arid regions, sand dunes, salt
marshes, and in other places where conditions of plant life
are exceedingly severe. Grasses range in height from less
than an inch, full grown, to more than a hundred feet.
Bamboos, the largest of grasses, form extensive forests
and jungles. In the mountains of tropical America and
Africa bamboos occupy a zone above timber line and be-
low the short-grass areas of the alpine regions. Some
bamboos have developed a climbing habit. Their slender
stems push up through the jungle along trails or streams
until they reach the sunlight. Whorls of branches then
develop which rest on the tops of the trees or shrubs and
support the main stem, which continues to grow and to
branch repeatedly until the plant forms a lacy curtain
hanging from the tree tops. One of the loveliest sights in
the West Indies and other parts of the American Tropics
are these curtains of bamboos on mountain side or stream
bank. Grasses love sunlight, hence only in dense forests
are they scarce. A few broad-leaved species carpet the
forest floor in the Tropics, and bamboos and others climb
out into the sunlight.

The greatest number of species of grasses are found in
the savannas of the Tropics, but the greatest number of
individuals are found in temperate and cold countries.
In the Arctic and Antarctic regions grasses compose about
a fourth of all the species. The grasslands of Alaska and
northern British America support great herds of caribou
and reindeer. On all the great mountain systems of the
world grasses are the dominant plants above timber line.

; [ 243 ]

GRASS

The great grass areas of the world are our own Great
Plains, stretching from the Mexican plateau to the Arctic
tundra; the semiarid llanos of Venezuela; the campos of
central and southern Brazil; the pampas of Uruguay and
Argentina; the steppes of Russia and western Asia; the
plains of Siberia, Mongolia, and China; the “sud” or ele-
phant-grass regions bordering the upper Nile, the veldt
of arid and semiarid South and East Africa, which sup-
ports the great game animals made familiar to us by moy-
ing pictures, and the steppes and savannas of Australia.
In such areas the grasses had their origin and have
reached their greatest specialization.

Visitors to Mariposa Grove, California, are told that
the big trees (Sequoia gigantea) are the oldest living things;
and in some of our museums are to be seen cross-sections
of Sequoia with the annual rings marked at intervals,
showing how thick the trunk was at the time of Christ, at
the discovery of America, and at other outstanding dates.
It seems very probable that individuals of some perennial
grasses may be quite as old as the big trees. Some marsh
grasses, like Spartina, and prairie grasses, such as buffalo
grass (Fig. 49), a dominant plant of the Great Plains,
propagate by~stolons or rhizomes, forming colonies over
large areas. Such plants are not only perennial, they are
practically immortal. Clumps of Spartina in our coastal
marshes may be branches of plants that grew from seed
thousands of years ago; and much of the buffalo grass
which today forms continuous turf for many miles is
probably part of the very plants that took ‘possession of
the plains as they dried after the retreat of the glaciers.

Bunch grasses, such as the grama grasses, often leave a
record of their gradual advance. The bunch grows by
accretion at the periphery, where successive stems arise,
there being no room for new stems within the bunch.
After a few years the center of the bunch dies, but the
periphery continues to advance until the colony assumes
the form of a ring. Such “fairy rings” are common on

[244 ]

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PLACE IN THE PLANT WORLD

the plains and in semiarid regions. Eventually the ring,
which sometimes becomes as much as a hundred feet in
diameter, breaks up into segments, but it can still be
traced by the circle of segments, which finally form the

eginnings of new rings. The increase in diameter of a

Fic. 49. Buffalo grass, pistillate and staminate plants spreading
indefinitely by stolons

bunch may be only a fraction of an inch each year, hence a
large fairy ring represents the growth of hundreds or even
of thousands of years.

Such. vigorous vegetative propagation enables grasses
to hold their ground once they have taken possession.
Their world-wide dispersal, however, is due to the numer-
ous devices they have developed for the dissemination of
their seeds.

Seeds of water grasses may be carried in mud on the
feet of water birds. Some are inclosed in air-tight cover-
ings that enable them to float. Darwin made an experi-
ment which shows how widely seed may be carried by
water, fishes, and birds combined. He threw seed of
barnyard grass into a stream, then caught a fish from the
stream and fed it to a stork. He planted the droppings
of the stork and barnyard grass came up.

More grass seeds are scattered by the wind than by any

[245 ]

GRASS

other method. People who have lived in the country
have seen tumble weeds, roughly spherical in outline,
rolling before the wind, scattering seeds as they go.
Many grasses scatter their seeds in this way. Tickle
grass and witch grass are familiar examples. The dif-
fusely branched panicle breaks away at maturity and is
whisked hither and yon, often piling up in fence corners.
One of the characteristic grasses of the Great Plains,
Schedonnardus paniculatus, bears its flowers on slender
branches along a narrow central axis. At flowering time
the axis may be only ten or fifteen centimeters long, but
the whole inflorescence continues to grow until at maturity
it is a loose spirally cciled affair as much as fifty centi-
meters long, which breaks away and rolls before the wind.

The commonest device for dissemination by the wind
is an attached tuft of silky or cottony hairs. The seeds
of the common reed (Phragmites communis), an ancient
and world-wide species, of plume grasses (Erianthus),
broom sedges (Andropogon virginicus and its relatives),
and many others float in the air like thistledown, and are
carried far and wide by the wind.

Some grasses secure dissemination of their seed by
barbed spines and spears that catch on the hair of animals.
Most needle grasses (Aristida), porcupine grasses (Stipa),
and others that steal rides in this way do no harm to their
involuntary carriers, but some, like sand burs, barley
grasses, and certain brome grasses are at times injurious.
In one of the needle grasses, Aristida longiseta, commonly
called dogtown grass because it grows in the loose soil
thrown up around the burrows of prairie dogs, the seed 1s
borne in a little needle-pointed spear with three slender
divergent bristles as much as ten centimeters long instead
of a shaft. The weight is so distributed that, as the little
contrivance is borne through the air the point is directed
forward, ready to strike into any animal in its way and thus
secure further transportation. At maturity whole swarms
of these seed bodies go scurrying across the plains.

[246 |

PLACE IN THE PLANT WORLD

Seeds, especially of annual grasses, are produced in far
greater number than can find place to grow. They fall
by chance in all sorts of places and all perish save the
relatively few that fall in unoccupied spots that meet their
requirements of moisture, temperature, and soil. A seed
contains a minute plant, the embryo, which was formed
while the seed was still attached to the mother plant.
Germination is a continuation of the growth which was
interrupted during the period of dispersal. While dormant
most seeds are dry and the seed coat is resistant to mois-
ture, thus preserving the contents. During germination
the seed coat swells and allows moisture to enter the seed.
The embryo sends out a little root in one direction and a
little stem in the other. The grain or kernel of the maize
well illustrates these processes because the seed is large
and the changes can be easily followed. The nourishment
for the embryo is stored mostly as starch, which is in-
soluble in water and can not be used directly by the young
plant. During germination the starch is converted into
soluble sugar, which can be transported by the juices of
the little plant. This sugar supplies food for the seedling
until it is able to get water from the soil through its de-
veloping roots and until its leaves turn green, ready to
manufacture its nourishment from the air by means of
the sunlight.

The mechanics of germination in the maize seed are
interesting. If the seed lies exposed on a moist surface
it merely puts forth a root and a stem. If, however, the
seed is buried in the soil the stem would have difficulty
in passing up through the soil as the tender tip would
be injured. The shoot does not bend and elbow its way
up as do peas and squashes and other dicotyledons, but
goes straight up, the growing parts, one little leaf rolled
up inside another, being contained in a tight pointed
sheath, closed at ae tip. This sheath (technically the
coleoptile) elongates, pushing upward through the soil
until it reaches the surface, when its tip breaks and the

[ 247 |

GRASS

shoot pushes through. There is, of course, a limit to
which this sheath will reach. In most kinds of maize it
can grow not more than about ten centimeters, though
there is a Mexican variety that can grow to the enormous
length of twenty-five centimeters.

There are one hundred and forty-seven genera of grasses
in the United States and about fifteen hundred species,
composing ten to twelve per cent of the entire flora. The
grasses of the world have been arranged according to their
relationships into fourteen tribes, of which all but one are
represented in the United States. The more important
are the following.

Bamboo tribe, including woody grasses, the most primi-
tive known. Primitive grasses are those in which there is
the least difference between the vegetative and the flower-
ing parts of the plant. Our only native bamboos are the
large and small canes (A4rundinaria macrosperma and A.
tecta) which form the canebrakes of the Southern States.

Fescue tribe, including fescues, bromes, blue grasses,
orchard grass, the common reed, pampas grass and other
relatively unspecialized grasses.

Barley tribe, including wheat, barley, rye, and our
native wheat grasses. The spikelets are borne on opposite
sides of a simple rachis.

Oat tribe, including oats and tall oat grass. The spike-
lets are borne in panicles. This tribe is especially well
developed in South Africa.

Timothy tribe, including timothy, bent grasses, needle
grasses (4ristida), and others having one-flowered spike-
lets in panicles.

Grama tribe, including grama grass, Bermuda grass,
buffalo grass, Spartina, and others with spies borne
in one-sided spikes.

Canary-grass tribe, including the fragrant vanilla grass
or holy grass, sweet vernal grass, reed-canary grass, an
important constituent of wild hay, and canary grass,
which furnishes canary seed.

[ 248 ]

PLACE IN THE PLANT WORLD

Rice tribe, a small group of which rice is the only im-
portant member.

Indian rice tribe, aquatic grasses with unisexual spike-
lets, including our wild or Indian rice.

Millet tribe, containing highly specialized grasses, in-
cluding two very large genera, Panicum (of which the
common European millet is a species) and Paspalum.
It also includes crab grasses, barnyard grass, foxtail millet,
pearl millet, and the vexatious sand bur. This tribe is
best developed in the Tropics and warm temperate regions.

Sorghum tribe, containing more highly specialized
grasses, including the great genus Andropogon (to which
belong the broom sedges), sorghum, sugar cane, and the
cultivated eulalia. The tribe is largely tropical.

Maize tribe, including maize or Indian corn, the most
highly specialized of grasses, teosinte, and Job’s tears.

Darwin says that a traveler should be a botanist, as
the landscape is so largely composed of plants. To know
them adds to the traveler’s enjoyment. Both the stay-at-
home and the traveler could add to their enjoyment of
landscape or garden by some acquaintance with grasses,
which are not so difficult to study as is generally supposed.
An illustrated work on the genera of grasses of the United
States can be purchased from the Superintendent of
Documents.?

1 Hitchcock, A. S. Genera of Grasses of the United States. U.S. Dept. Agr. Bull.
772. Supt. Doc., Govt. Ptg. Office, price 60 cents.

SELECTED BIBLIOGRAPHY

Cuase, Acnes. First book of grasses; the structure of
grasses explained for beginners. New York, 1922.

Hircucock, ALBERT S. A text-book of grasses, with
especial reference to the economic species of the
United States. New York, 1914.

—— The genera of grasses of the United States, with
especial reference to the economic species. U. S.
Dept. of Agr. Bull. 772. Washington, 1920.

[250]

Part V

DESERTS AND THEIR PLANTS
By
DanIEL TrRemBLy MacDoucat

Research Associate
Carnegie Institution of Washington

CHAPTER I
CHARACTERISTIC FEATURES OF DESERTS

Deserts make up as much as one-sixth of the total land
area of the world today; and those now shown on the
maps are not all the places that have been arid at some
time in the long history of the earth. Rocks, salt beds, and
wind-blown deposits bear evidence that many regions
now moist and fertile have lacked rainfall for long periods
of time. Uplifting and lowering of land masses, causing
deflection of winds, have brought about a deficiency of
rainfall in areas previously well watered and abundant
rainfall in others that had been bleak deserts for thou-
sands or maybe millions of years.

Generally such changes take place so slowly that they
are difficult to measure in terms of human history, but
evidence that certain regions in northern Africa and cen-
tral Asia have been receiving progressively less rainfall
during the last five or ten thousand years seems to be
accumulating. However, geographers are by no means in
accord on this matter. Those who advocate the theory
of desiccation do not hold that every year has been a
period of less rainfall than the preceding one, but that de-
crease has alternated with increase, so that although the
yearly rainfall has been less at the end of a thousand-year
period, for example, than at its beginning, there may have
been during that period increases continuing through a
half or even a whole century.

Whatever truth there may be in the theory that great
areas of the earth’s surface are growing more arid at the
present time, we have plenty of full-blown deserts to

[253 ]

DESERTS AND THEIR PLANTS

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[254]

CHARACTERISTIC FEATURES OF DESERTS

supply us with our subject matter—the special plant life
found in such arid lands (Fig. 50). For the life of desert
regions—whether plant or animal—is distinctive. It dif-
fers both in appearance and habits from the life of moister
environments. The differences are adaptations that are
always advantageous and sometimes indispensable to ex-
istence in the desert. That the desert molds organisms to
a higher degree of fitness for life under the trying conditions
it presents can not be proved; but if anything in the vast
accumulation of data on plant history is certain, it is that
plants which do not show certain specialized structures
and habits will die out in dry regions.

Perhaps the development of the peculiar structures and
organs of the xerophytes—which is the name for plants
able to live with little water—originated as a direct re-
sponse to the vital needs of plants in arid regions; or per-
haps modifications which better fitted them to an exis-
tence in such regions appeared merely by chance in certain
strains or individuals, enabling them to survive while other
forms not so adapted died out. Just exactly what
agencies caused the whale and the seal to develop into
organisms fitted for life in the salt seas, or the cactus and
thorn plants to develop into organisms adapted to con-
tinued existence in deserts, is not known. But however
this may be, like the whale and the seal, the xerophytes
of deserts are where they belong. To see why this is so,
we must consider the special conditions of climate and soil
peculiar to deserts.

CLIMATE OF DESERTS

Perhaps the phenomena which most directly bring
about desert conditions and so are most characteristic of
deserts are scantiness of rainfall and the irregularity of its
occurrence throughout the year or from season to season.
Thus, in the moister regions of the tropic and temperate
zones, where broad-leaved plants form a prominent part
of the perennial vegetation, the total rainfall in any year

[255 |

DESERTS AND THEIR PLANTS

is never more than two or three times as much as it may
be in another year. In deserts, on the other hand, no rain
at all may fall within a certain year, while several inches
may fall in the following year, making the ratio between
the maximum and minimum yearly precipitation very
high.

The relation of the rainfall to the possible evaporation
must also be taken into account. Water from rain satu-
rates the surface layers of the soil; and some of it may, and
generally does, percolate deeply, with the result that in
moist climates the percentage of moisture increases until
a depth is reached at which the water occupies all of the
spaces between the soil particles. The upper limit of the
portion of the ground wholly saturated with water is
known as the water table. The water table as such does
not exist in desert regions, or at least it exists only in a
greatly modified form. The run-off from the steeper
mountain slopes passes to levels deep under the surface,
their depth being determined chiefly by layers of hardpan
and other semipermeable material, or by clays and their
like. Low-lying basins, such as the oases of northern
Africa and the below-sea-level basins of the Colorado
River desert, Death Valley, and connected basins in
California, are underlain by bodies of water which may be
reached by boring, but these reservoirs are not fed by pre-
cipitation on the surface directly above.

Rainfall in the desert results in wetting the surface of
the soil to a depth of only a meter or two. It is from the
moisture held in this shallow layer that true desert plants
derive their chief supply. As the water in the surface
layer has no connection with and is not fed by the deep
underground water supply, it naturally follows that
evaporation from the surface layer is a very important
factor in determining the moisture content of the soil
and the practical value to plants of such surface-restricted
rainfall.

The rate of evaporation depends largely on the temper-

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CHARACTERISTIC FEATURES OF DESERTS

ature and upon the total amount of wind flow. To compute
this rate, standardized measures have come into use, such
as narrow cups of baked clay 15 centimeters long and
about 2.5 centimeters across the top, holding 50 cubic
centimeters of water. The rate at which water evaporates
from the surface of these cups varies with changing winds
and temperatures and furnishes the observer with a parallel
from which to calculate the rate of evaporation from the
soil. Measurement of the amount lost by evaporation
from the surface of water in a shallow tub will also give a
general indication of what is happening in the soil, al-
though the amount of water which passes off as vapor from
a square meter of soil is never as great as that which passes
off from a water surface of equal area. The “evaporating
power” of the air at a given locality, as it has been termed,
may be used in determining the degree of aridity of that
locality. When in any region this evaporating power
is so great that the amount of moisture which may be
lost from a water surface is greater than the amount re-
ceived by rainfall, some of the phenomena ordinarily
associated with deserts will occur. Thus Salton Lake
(Plate 51), in the desert of the Colorado River basin,
may lose as much as eighty inches in depth within the
year, while the rainfall may range from zero to two inches
only. At the end of this article (pages 282, 283) there are
appended tables prepared by Dr. W. A. Cannon to show
the relation of evaporation to rainfall at several localities
in the Algerian desert during 1908, from which it may be
seen that during April the evaporation in the desert at
El] Oued was 629 times as great as the precipitation. A
careful perusal of these tables shows that in the littoral
zone of Algiers, including the city of Algiers, evaporation
may be from one to three times as great as rainfall; and in
the interior deserts the total evaporation for the year is
as much as sixty-three times as great as the precipitation.

But neither the total rainfall nor the ratio of the
evaporation to the rainfall can be regarded as a direct

[257]

DESERTS AND\THEIR: PLANTS

index to the amount and character of the vegetation in
deserts, because the rainfall of deserts is very irregular
both in occurrence and quantity. Thus, the rains may
come in torrential storms, in which a large part of the
water runs off in floods and does not moisten the soil in
proportion to the amount of precipitation; or they may
come in frequent slight showers, the water from which, fall-
ing on a dry and heated soil, is quickly vaporized; in either
case the benefit to vegetation is difficult to estimate.
Again, if the rains come in the cooler season (as they do in
the Mohave desert), when the temperature is unfavorable
to vegetative activity, the plants derive no immediate
benefit; and later, with the advent of their growing season,
they will respond only to such moisture as still remains in
the soil.

So much for rainfall. As for temperature, deserts are
proverbially both dry and hot. The extremely high tem-
peratures that are common in deserts occur over areas of
land which lack moisture and so can not be cooled by
evaporation. And not only may the temperature of the
soil and air of arid regions be very high at certain seasons,
but also the variation or range of temperature from low to
high may be very great. The greatest ranges of tempera-
ture are found near the centers of continental land masses,
where the air is very dry and hence highly transparent to
earth radiation into space. Turkestan is a region which
typifies these conditions. At Kazalinsk a range in tem-
perature of 158° Fahrenheit (88° centigrade) has been
recorded between summer and winter, and it is reported
that at other stations in this region the difference between
the minimum and maximum temperature is sometimes as
much ‘as 180° F. (100°'C.),

As excessive heat seems to offer the greatest trial to man,
and must act as a limiting condition to the activities of
beast and plant, it may be of interest to mention here
some localities where especially high temperatures have

been recorded. Such are Wadi-Halfa, Egypt, on the
[258 |]

CHARACTERISTIC FEATURES OF DESERTS

middle Nile, where 130° F. (52.5° C.) has been noted, and
Bagdad, California (a small station in the desert of the
Colorado River basin just west of Needles), where a
maximum of 132° F. (54° C.) has been reached. Similar
temperatures have been recorded in Death Valley, Cali-
fornia, which lies below sea level and extends eastward
from the base of the Sierra Nevada.

As one would expect, the surface layers of the soil of
deserts are several degrees warmer than the air after mid-
day. In some places this difference in temperature may be
as much as 45° F. The desert traveler soon learns that
guns, tools, and all other metal objects, if exposed to the
sun, may be handled only with great discomfort during
the midday period. The horseman who happens to dis-
mount at noon may save himself some discomfort if he
covers his saddle, so as to shade it from the direct rays of
the sun, or, better still, removes it and allows evaporation
to cool the back of his mount and dry out and cool the
bearing surface of the saddle. The top layers only of
the soil in deserts hold the absorbing roots of their plants,
and yet these layers often reach a temperature of 130°
150° F., if we may judge by common reports. Buxton
reports a temperature of 122°-140° F. (50°-60° C.) for
soils in Palestine, of 172° F. (78° C.) for a sand dune in
the Sahara, and, most remarkable of all, a temperature
of 183° F. (84° C.) for soil on the Atlantic coast near
Loango, French Equatorial Africa.

We may well ask, “What is the effect of such tempera-
tures on living cells?” The protoplasm of some specialized
organisms which live in hot springs is attuned to with-
stand great heat, but most organisms will suffer harm if
subjected to a temperature above 140° F. (60° C.). Seeds,
however, are not damaged by heat of that degree, nor are
plants at those periods when their organs are dormant. An
organism’s resistance to high temperatures depends
primarily on the proportion of water to other materials
in its make-up, and secondarily upon the composition

[259]

DESERTS AND THEIR PLANTS

of those other materials—that is, on how highly specialized
they are in their heat-resisting properties. Protein (an
essential constituent of all living cells, familiar to us in
the form of white of egg, in which it exhibits its typical
properties) coagulates at the highest of the temperatures
just mentioned; so it may be assumed that death from
heat involves similar changes in plant and animal tissue,
although other alterations equally deleterious may take
place simultaneously. The actively growing layers in a
plant may normally contain as much as 99.5 per cent of
water; excessively high temperatures would cause evapo-
ration at a rate so high that the necessary proportion of
water could not be maintained and desiccation and death
would result. In some experiments on plants at the Desert
Laboratory at Tucson, Arizona, the heat of the sun was
supplemented by that radiated from electric heaters. The
flattened joints of Opuntia were found to continue growth
in temperatures as high as 137° F. (58° C.). When the
growing layers were heated still further—to 146° F.(63° C.)
—no damage resulted to the plant, but growth ceased
and was not resumed until the Joint was cooled to 122° F.
(50°C.). Opuntia is well adapted to endure daily ex-
posures to direct sun over long periods. The protoplast
of its cells has a high content of mucilage, such as is found
in gum arabic or agar, which undergoes little change when
subjected to a temperature as high even as its boiling
point in water. It is to be noted, also, that seeds which
lie on the surface of the soil not only survive a hot season
several months long but may endure several such seasons
and still germinate. Although subjected to extreme heat,
the protoplasm underneath their tough coverings 1s but
little affected, because it is inactive and low in water
content.

Such immunity from excessive heat is not possessed,
however, by lizards, beetles, and other small animals
which stay on the surface of the soil or in the layers of loose
soil just beneath the surface or traverse the flat faces of

[ 260 |

CHARACTERISTIC FEATURES OF DESERTS

rocks exposed to the direct rays of the sun and whose
bodies must therefore be of almost the same temperature
as the soil. It may be safely assumed that the protoplasm
of these animals remains more or less active through a
range of bodily temperature of more than 100° F., as they
lack the controls which maintain the body temperatures
of higher animals within a narrow range. Even in such
warm-blooded animals as man, however, variations in
bodily temperature as great as 14° or 15° F. are reported.

So far no mention has been made of low temperatures in
arid regions, but these also are to be encountered in the
deserts of the trans-Caspian region, in certain dry tracts
throughout north-central Asia, and in the dry regions of
northwestern North America.

Deserts experience great heat and much of it, for since
they have so little rainfall it follows that the actual total
number of hours of sunshine in deserts in a given period
may be but little less than the possible total number. And
not only do the sun’s rays pour down on the desert soil
from an unclouded sky, but the relative humidity (amount
of water vapor) in the air, is very low, so that the rays of
the solar spectrum which reach the earth are made up of
waves of the higher frequencies, or shorter wave-lengths.
Some screening effect is exerted by dust particles, the
quantity of dust depending upon the wind flow. At times
volcanic dust is blown into the upper air, blanketing great
areas of the earth’s surface for long periods and screening
out or obstructing completely the passage to such areas of
some of the rays at the blue-violet end of the spectrum.
It is these blue-violet rays, together with the ultra-violet
ones (which are not visible), which produce the most
direct effect on living tissue. Only recently have scientists
realized the importance of the ultra-violet rays to plant
and animal organisms, and especially to the latter. Green
plants, particularly large ones with leaves, seem less sensi-
tive to these invisible rays; but small plants with thin
skins respond quickly to them, as do the higher animals.

[ 261 |

DESERTS AND THEIR PLANTS

Deserts provide the most intensive exposure to ultra-
violet rays; hence they are largely visited by health
seekers.

Sor, oF DESERTS

The soil of deserts is as distinctive as is their climate.
Since the surface is devoid of that mat or carpet of vegeta-
tion which in other regions holds the particles of soil to-
gether, forming a “sod,” and since, also, the particles of
desert soil are too dry to cohere of themselves, even a
very slight wind will suffice to stir up and shift the material
of the surface layers. The most familiar topographic fea-
ture resulting from wind action 1s the sand dune (Plate 52).
In a sandy area whose surface layers are made of hard
particles of almost uniform shape, size, and weight, the
wind shifts the sand and piles it up in mounds or dunes of
more or less regular form. Furthermore, the wind is con-
tinually picking up the particles on the exposed side of the
dune and carrying them to the summit, whence they may
roll down the lee side. thus making it steeper than the
windward side.

Rock surfaces, when subjected to gusts of wind laden
with sand, are smoothed, carved, and fluted by the cor-
rasive action of the pelting sand grains. Another char-
acteristic feature resulting from wind action is the desert
pavement, which begins as a surface made up of small
rocks, gravel, sand, and dust. The wind removes the
smaller and lighter constituents from between the larger
and heavier ones, so that the heavier ones are allowed to
sink. After this process has continued for many years, the
pavement becomes an irregular mosaic of rocks, which
may vary in size from a small pebble to stones as large
as the closed fist and whose surfaces have been polished
by the action of the moving grains of sand.

In addition to altering the surface, wind action in
deserts is responsible also for the rounded outlines of
small hills, mounds, and even artificial structures, as 1s

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CHARACTERISTIC FEATURES OF DESERTS

evidenced by certain ancient stone structures in the
Libyan desert, whose right-angled corners have been worn
away by the abrasive action of wind-borne sand. While
on an extensive journey with a camel caravan in this
desert, I encountered many rounded hillocks like those
illustrated in Plate 53. Ages of attrition by flying sand
have streamlined these hills so that the wind flows by
them with very little obstruction, forming an eddy on the
lee side such as forms in the sea in the wake of a ship.
Such hills offer very little shelter from the direct force of
sand storms.

A consideration of the special conditions peculiar to
deserts must include some notice of alkaline and salty
soils and of dry lakes. In regions with adequate rainfall
the run-off collects in streams and fills natural basins to
their rims, thus forming lakes, whose waters may ulti-
mately find outlets to the sea. A continuance of this
process of stream and lake formation results in complete
systems of drainage such as are found on each of the con-
tinents today. In arid regions, on the other hand, there is
not enough rainfall for the run-off to fill the natural
basins to their rims, so that the lakes (if any form) are
shallow and have no outlets; such streams as reach the
sea run their full courses only intermittently, and the
others lead into great shallow basins.

All drainage waters, including those which slowly per-
colate to the lower levels of the earth’s strata, carry salts
which have been dissolved from the soil. The salt of the
sea has such an origin. In incomplete drainage systems
the salts carried by the run-off waters are deposited as
layers in flats or basins, or else accumulate 1n inland lakes
or seas and make saline the waters of such large bodies as

Great Salt Lake in Utah.

CHAPTER II

ORIGIN AND DEVELOPMENT OF DESERT
PLANTS

Ir is in an environment resulting from the meteoric
(atmospheric) and edaphic (soil) conditions described in
the preceding chapter that plants and animals exist in
deserts. In the scantiness and irregularity of its rain-
fall, the wide range of temperature of its soil and air,
its low humidity, its high intensity of sunlight (with
especial reference to the rays with the shortest wave
lengths in the ultra-violet), the greater ionization of its
atmosphere, the greater salinity of its soil, and its pro-
nounced wind action—in all these aspects of environment
deserts offer to plants and animals conditions of living
widely different from those encountered in the moist,
well-watered regions of the tropic and temperate zones.

So rigorous are the requirements of life in deserts that
most of the plants native to the more humid regions can
not survive there. The most notable examples of the suc-
cessful growth in arid lands of plants native to moist
regions are orange and lemon trees, common crop plants,
and certain tender vegetables; but all of these must be
cultivated in soil which is irrigated by water from wells
and diverted streams. These plants would in no wise
survive without the most intensive and meticulous
farming.

But plants and animals which are native to deserts find
the conditions of life there acceptable. They display
modes of activity suited to the climate and soil and, pre-
sumably, have developed or were evolved under the same

[ 264 ]

DEVELOPMENT OF DESERT PLANTS

conditions as those which now prevail in these regions.
The characteristics of these native desert organisms con-
stitute one of the most interesting phases of biology.

Weird and grotesque as some of the plants which in-
habit the deserts may seem to us, they are none the less
in harmony with their surroundings, or at least as nearly
so as are most other living things. It is customary, in
speaking of a plant which flourishes in a given locality, to
say that it “grows like a native.” This is assuming that all
species of plants are now to be found in the places best
suited to them. No assumption could be more fallacious.
The fact that plants which man has transported from dis-
tant places often run riot and become weeds and serious
pests in their adopted pastures and fields is a signal refuta-
tion of this too general statement. And many wild species
left in their native habitats may be dwindling and moving
toward extinction because of some deleterious agency in
their environment which we do not apprehend or have not
taken into account.

Plants, like human beings, are found in those localities
which they have happened to reach, in which they can
endure season after season, and in which they can repro-
duce themselves. And the vegetation of deserts is no ex-
ception to this rule. The fact that the desert environ-
ment is unusual and trying, perhaps, to most plants does
not mean that all of the species found in arid regions are
under greater stress than all of those found in woodlands
of the Mississippi Valley. In fact, most species char-
acteristic of deserts suffer notably when taken into what
might seem more favorable environments. It is by no
means to be taken for granted, for example, that the
plants of deserts would be benefited if furnished more
water. The regulation and restriction of the water supply
of succulents transplanted from Mexican, South American,
or African deserts to moist regions is, in fact, one of the
most difficult problems in gardening.

The peculiar forms of plants which endure or even thrive

[ 265 |

DESERTS AND THEIR PLANTS

in deserts may be best understood in the light of their
origin and development. The primitive ancestors of all
plants probably began as simple masses of protoplasm in
water, or in water-saturated sand or small fragments of
rock; for, in the beginning, there was no soil. Accumula-
tions of small water-worn bits of rock made sandy beaches,
or particles even smaller might be blown about by the
wind and piled up in dunes; but of humus, or the softer
material of the ground, as we know it today, there was
none. Soil could come only after plants with hard, woody
tissues and animals such as beetles, with durable con-
stituents, had left their remains on the surface to slowly
disintegrate; for the surface layer which we know as soil 1s
a mixture of minute bits of rocks and of fragments of dead
plants and animals in various stages of decay and dis-
integration.

The progenitors of plants, whatever form their bodies
might take, were composed largely of water—perhaps as
much as 99/4 parts in 100. If for any reason they became
exposed to the air they dried out and perished. Not only
in this did they differ from the modern plants, but also 1n
their ability to multiply by the division of one simple mass
into two, as a large drop of water separates into two or
more smaller drops. While we do not have the evidence
to show all of the intermediate steps, yet it is known that
after a long time these simple early plants developed
special methods of reproduction. The entire body was
no longer concerned with the process, but certain masses
or cells were differentiated and specialized to perform
this function. These specialized reproductive cells, or
spores, became detached from the body of the plant and
could move about only in water and germinate only when
immersed. The next step was the further differentiation
of the reproductive cells into two kinds, male and female,
constituting sex and making it necessary for the two differ-
ent kinds of reproductive cells to come together and fuse
in order to produce new individuals. Forms as high in the

| 266 |

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DEVELOPMENT OF DESERT PLANTS

scale of plant life as ferns, liverworts, or mosses might have

evolved from the first plants near pools or stretches of
shallow water or in moist sands, especially in regions char-
acterized by continuous fogs or heavy clouds. Vegetation
in those early days, however, no matter how abundant it
might be, still could not venture away from the shores and
banks of streams and lakes, and might even occupy ex-
tended areas of shallow water, which, with their accumu-
lations of dead stems and other débris, must have re-
sembled a modern swamp.

Thus the greater part of the land surface of the globe
was still inaccessible to plants, which could not exist far
away from bodies of water. A further very marked step
in evolution was necessary before plants could spread
across the country and occupy in some fashion or other
almost the entire face of the earth between the polar
regions. While still living in swamps, the fernlike plants
had developed a life cycle which included two generations.
An example of one of these generations is the ordinary
plant known as a fern, which is asexual and produces
the familiar brownish spores. The spore germinates and
produces an inconspicuous organism recognizable as a
fern by the specialist only—a prothallium, as it is termed,
which must have abundant moisture to thrive. The
prothallium is thin, flattish, and green, and may be so
small that it can be covered by the letter o of this type.
The two kinds of reproductive cells known as the sperm
and the egg are produced in special sex organs on the
under surface of the prothallium, and the sperm cell
must swim from its place and fuse with the egg cell in
order to fertilize it. The germination of the egg results
in the larger fern as we commonly know it. Now it is
obvious that a plant which needs two such forms, one of
which must live in a very moist locality, must be confined
to the waterside if it is to complete its life cycle and repro-
duce itself.

Not until the larger plants acquired the more delicate

[ 267 ]

DESERTS AND THEIR PLANTS

bisexual generation and protected it from desiccation was
it possible for them to get away from the swamps and
streams and develop into the more highly specialized
forms. This they finally accomplished. All the large
modern seed plants, such as trees, shrubs, and herbs, are
homologous to the fern. Unlike the fern, however, the
spores from which the gametophyte (generation which
bears sex organs) of seed plants is produced are deeply
buried in the flower tissues, and the whole process of re-
production is carried on inside of structures in which the
elements fusing to form the fertilized egg are shielded not
only from desiccation but from other deleterious agencies.
Once the sporophyte (generation which bears asexual
spores), as illustrated in the fern, had developed the
gametophyte and acquired the ability to carry it safely
protected within its flower structures, the plant was ready
for its pilgrimage across the high open stretches of the
earth. The first time that a plant accomplished this feat
marked the beginning of one of the great epochs in biologi-
cal history. For animals are dependent upon plants for
food; and until the plants began to move from the well-
watered areas out upon drier land, animals too were con-
fined to the waterside.

Up to this point in our discussion we have thought of
the necessities of reproduction alone as governing the
evolution of plants, but it is plain that the occupation of
drier lands brought up other problems in plant life also.
Root systems which were adequate for anchoring the
stems in moist places and for taking up water from ground
in which it was abundant would hardly suffice in arid
regions, where the moisture might be in the surface layers
only on days immediately following rains or might run
deep underneath a thick layer of soil in which the oxygen
supply necessary for plant growth was very scanty.

A leafy plant which is to survive in a desert must not
only have roots which can pick up the precarious water
supply, but it must restrict its use of such moisture as it has

[ 268 |

DEVELOPMENT OF DESERT PLANTS

picked up. The extent to which a plant may use the
energy of sunlight depends in the main upon the area of
green surface that it can expose to the sun’s rays. But
the greater the surface exposed to the air, the greater the
loss of water by evaporation. However, evaporation
compensates in a large measure for this loss by a good
service it performs at the same time. For the photo-
synthetic action of the green cells requires a continuous
flow through the stem of the water, or sap, picked up by
the roots, which holds in solution the nourishing salts of
the soil; and evaporation in the walls of cells exposed
to the air is the force that pulls the sap upward from the
soil. A thousand pounds of water must be lifted for every
pound of dry matter laid down in the aerial tissues of a
plant, and evaporation is the agency that does this
mighty work.

A leaf is therefore a sun-driven factory in which water
must be evaporated in sufficient quantity to lift solutions
from the soil, and in which some of the water of the soil
solutions enters into chemical combinations used in the
nourishment of the plant. In moist regions the capacity
of the leaf factories 1s probably limited only by the num-
ber of hours of sunshine received and its intensity; for an
adequate water supply is always at hand. But in arid
regions, where the sunshine is always adequate, the
capacity of leaf factories depends directly upon the amount
of water which the plants may secure from the soil, a
workable proportion of which is present only during cer-
tain seasons.

It seems abundantly clear that the first plants lived in
the moister regions, and that not until species appeared
with specialized root systems and with water-conserving
green organs was a notable amount of vegetation to be
found in deserts. This is emphasized by the fact that no
fossils have ever been found of plant types which we
recognize as suitable for existence in very arid regions.
The nearest approach to such types is seen in the hard

[ 269 |

DESERTS AND THEIR PLANTS

leaves of the cycads and in pine needles, whose fossil
prototypes probably have been preserved; for genera with
similar leaves are well represented in the paleontologic
record. It is therefore reasonable to suppose that these
were the first of the higher orders of plants to occupy the
parts of the earth’s surface not so well watered as the
regions with abundant rainfall. It is true that the climate
and soil of deserts are not in the main favorable to the
preservation of fossils, although the alluvials along the
streamways might be counted upon to entomb and pre-
serve some of the more durable structures; and the heavy
spines of such desert plants as the cactus and other thorny
shrubs contain a high proportion of calcium and silica and
should be as capable of preservation as the bones of
animals. Rich finds of animal skeletons and of shells have
been uncovered in arid deposits, but so far nothing sug-
gestive of the metal-hard spines of the tree cactus has
come to light.

[ 270 ]

CHAPTER III

ADAPTATION OF PLANTS AND ANIMALS
TO DESERT CONDITIONS

Ir would seem, therefore, that the characteristic plants
of the deserts of today are of very recent development, and,
in one sense, represent the highest specialization of which
the leafy shoot of seed plants is capable. For it must be
understood that before the desert species appeared plants
with erect stems and many branches bearing broad-bladed
leaves had developed; and these could thrive on solid
ground, instead of only in swamps, as was true of the first
plants. From these early land-dwelling forms desert plants
evolved. An intimate study of the structure and habits
of xerophytes, or desert plants, brings to light two marked
characters not displayed by their ancestors, or, at least
not displayed by plants of the same species living in well-
watered regions today. Whatever the agencies which
started a species or strain of plants toward modification
of its structure and habits so as better to equip itself for
living in dry regions, these two characters in thousands
of species of the higher or seed-forming plants bear evi-
dence that such modification has taken place. They are,
first, the possession of thorns and spines rather than
branches and leaves, and, second, succulence (Plate 55).
Let us now consider briefly how these two characters may
have been acquired.

MopIFICATION OF LEAVES

The first and most noticeable reaction of a leafy plant
to an arid environment is its failure to attain that ex-
pansion of leaf surface which it might attain in a moist or

[271 |

DESERTS AND” THELR (PLANTS

humid region. Take, for example, a pair of rapidly grow-
ing sunflowers. Allow one to develop in a moist green-
house in a well-watered pot and cultivate the other in a
dry house such as would be suitable for growing succulents.
The total area of leaf surface will be much less in the
plant left in the dry house than in that which was copt-
ously watered. However, it must not be taken for
granted that the plant species now found in deserts have
resulted from an experiment by nature as direct and sim-
ple in its effects as that described above. So far as any
experiments yet made by man have divulged, the direct
effect of a new environment on the organism of a plant
(in this instance, restricted leaf surface) is not trans-
mitted by the seeds to the succeeding generation. The
seeds of the sunflower grown in the arid environment,
if germinated in a moist house, would produce plants as
broad-leaved as those of any other sunflower. In other
words, change of environment does not establish heritable
characters in a plant.

Now, the primary function of stems and branches is to
support the weight of the leaves, which contain the vital
chlorophyll. And so it follows that lessening the total
spread of its leaf surfaces, as the xerophyte has done,
renders unnecessary as many branches as are required by
a plant with wide leaves. To illustrate: Take a profusely
branched shrub bearing many large leaves, such as is
common in the moist temperate zones. Remove some of
the leaves, and trim away the margins of those that re-
main until they are much reduced in size. Then cut away
the smaller branches or twigs (which, since the leaf sur-
face is lessened, are no longer necessary), and reduce the
size of the remaining branches. The resulting specimen
is something like a thorny, desert shrub. And even the
spiky appearance of the xerophyte may be produced by
paring away the outside layers of the branches until their
tips are sharp pointed. The spinosity of a desert shrub
is further accentuated by the fact that not only does its

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ADAPTATION TO DESERT CONDITIONS

stem contain rigid woody tissue, but the outer layers of
its spines also (which are entirely of cellular tissue), are
indurated by a growth of woody material in their cell
walls and by a deposit of calcium and silica in their cell
cavities.

In many spinose xerophytes a layer of waxy material,
also, is formed on the surface of all the external organs,
including the leaves, thus lessening further the rate at
which water may evaporate from the plant. Spinose
plants exemplify the earliest and the most fundamental
changes by which plants of moist regions have altered so
as to become capable of living in regions with a scant
supply of water in the soil and with little rainfall. They
are the most abundant and widely distributed of all
desert species. Plants in any family may show modifica-
tions of this kind.

SUCCULENCE

The second marked character developed in desert plants
by modification is succulence, or the quality of having
juicy or watery tissues (Plate 57). To acquire this char-
acter it was necessary for the early plants to form large
masses of specialized tissue in their roots, branches, or
leaves for the storage of surplus water, available in times
of failure of outside sources.

These two changes—reduction of surfaces exposed to
evaporation by a modification of branches and leaves into
thorns and spines, and the acquisition of the quality of
succulence—may have taken place simultaneously in
some plant species. While the shoot and leaves were
gradually diminishing their surface extent, certain of their
tissues, such as the medulla (or pith) and the cortex (or
epidermis), may have been enlarging so as to increase their
capacity for water storage. The Meseméryanthemum and
Sedum are typical plants which have such enlarged tissues
in their leaves. The most extraordinary types result when
the surface-reducing tendency and the swelling of the

[273 |

DESERTS AND THEIR PLANTS

water-storing tissues are carried to the extreme in the
same individual, as in some of the Cactaceae and Euphor-
biaceae. Continued reduction of a shoot will eventually
bring it down to a thin cone; and the exaggerated enlarge-
ment of its pith or cortex, if carried far enough, will cause
the stem to swell out into a fleshy cylinder or globe of
irregular outline. This seems to be about what has hap-
pened in the long evolutionary history of such a plant as
the barrel cactus of the deserts of Mexico and the south-
western United States. In this bizarre plant the woody
cylinder of the stem is no larger than the forearm of a
man, although the swollen cortex surrounding it is several
inches in thickness. The epidermal, or outer, layer of the
stem’s covering is heavily waxed to prevent the escape of
water. The hard, curved spines, which are the vestiges of
foliar organs of an earlier period, suggest that the ancestors
of this plant had a branched shoot. Perhaps as many as
two thousand species of cactus and other plant families
show a development toward this type, which may be
said to have reached its extreme specialization in the
barrel cactus (Plate 58).

A comparison of the conditions under which spiky
plants grow most abundantly with those under which
succulents reach their highest development reveals some
interesting correlations. Thus it is noteworthy, in regions
in which the rainfall is very slight and uncertain, such as
the great desert areas of northern Africa and of Asia, that
the dominant members of the scanty flora are spiky
shrubs or tough herbs which spread only a limited expanse
of leaf surface to the evaporating force of the sun and
wind (Plate 59). The rainfall in such regions never comes
in sufficient quantity to allow the plant to take up a
supply of moisture in excess of its immediate needs; or
else it arrives at a time when the plant is not capable of
taking up an excess. The root systems of these spiky
shrubs ramify through the loose soil and penetrate into
the crevices of rocks, gathering in minute supplies of

[274]

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ADAPTATION TO DESERT CONDITIONS

moisture from a comparatively extensive area of soil.
When the proportion of moisture in the soil falls so low
that only oven heat could extract the tightly held remnant,
the acquisition of water by the plant goes on very slowly.
In fact no absorption at all would be possible were it not
for the osmotic action of the highly concentrated sap of
these plants. Laboratory tests show that the sap of some
xerophytes has an osmotic pressure of a hundred and fifty
to two hundred atmospheres, or three thousand pounds to
the square inch. The absorptive or sucking power of the
cells in plants of such highly concentrated sap would be
sufficient to raise a column of water six or seven hundred
feet. Such energy, tremendous as it seems, is necessary
for plants which exist in the extremely dry soils of deserts.

The possession of the power of suction to a high degree,
however, does not entirely solve the problem of taking
water from a soil which holds but little of this indispensable
element on its minute particles by the strong grip of sur-
face tension. The soil particles are at all times slowly
disintegrating. The complex union of chemical elements
which form rocks is constantly being broken up into solu-
ble salts of sodium, magnesium, calcium, potassium,and
other elements, which dissolve in the minute layers of
water from which the plant must draw its supply. These
salts are being continually carried off in a moist region
by the sloping drainage, but in the low basins and level
plains of deserts, which lack drainage, they must remain;
consequently the soil becomes highly charged with soluble
salts. If at the same time the chemical combinations in
the soil are such as to make it “alkaline” only a compara-
tively small number of plant species may survive. For
the highly concentrated saps of the plant cells are “acid,”
that is, they hold free hydrogen ions in solution. In the
alkaline soil solutions, on the other hand, an opposite
condition prevails; for all of the hydrogen content is
firmly bound to oxygen, so that free hydroxyl ions are
present instead of free hydrogen ions.

[275 |

DESERTS*AND ‘THEIR’ PLANTS

The absorbing cells of the plant must therefore suck
up their “‘sap” from a soil solution which is not only
alkaline but which contains a higher proportion of salts
than can be utilized, and at the same time the acidity and
osmotic pressure of the sap must be maintained—a seem-
ingly impossible task. The plant’s problem is to isolate
water from a solution heavily charged with deleterious
ingredients. It is as if a thirsty man were given a fascicle
of lemonade straws through which to suck and told to
extract a pleasant-tasting drink from a briny pool. Now,
to accomplish this, he would need a chemical screen that
would obstruct the passage of the undesirable constituents
while admitting the desirable ones; but no such screen has
ever been devised by man. If one is ever invented it will
be of incalculable value in obtaining fresh water along
many thousands of miles of arid and torrid seacoasts.

But though man has not solved this problem, desert
plants have. They have a process for extracting fresh
water from briny and alkaline solutions and are thus
capable of living in black alkaline soils and in the white
and salt-encrusted areas around dry lakes and inclosed
basins. According to results of experiments which I have
made with capsules of cellulose, mucilage, and gelatin,
whose properties simulate some of the activities of the
living plant cell, this screening action of xerophytes 1s
made possible by the presence of certain lipoids, or com-
binations of fatty substances with phosphorus in their
cells.

Succulent plants are obviously best suited to places in
which there is at times an abundance of water which may
be taken up and stored. This condition prevails in the
arid regions of North America; and the cactus, which is
common to these regions, is a striking example of a water-
storing species. In regions well away from the seacoast,
or in places where a “‘continental’’ climate prevails,
periods of plentiful rainfall may occur in midwinter and
in midsummer, although the total amount received an-

[ 276 |

PLATE 59

Watering domestic animals from supply obtained by digging pits in sandy stream bed in Upper Egypt.

The spiny shrubs are typical of North African deserts

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ADAPTATION TO DESERT CONDITIONS

nually may be small. However, the soil is thoroughly
wetted during the rainy seasons, and at such times con-
siderable water may run off through the intermittent
streams, which have dry beds during most of the year.
Heavy rainfall during restricted periods does not alone
insure the proper development of succulent plants. This
fact is strikingly illustrated by a comparison of the deserts
of Sonora (Mexico) and southern Arizona with the
Mohave Desert, which is the southernmost of the series
of arid basins in southwestern North America and which
includes the famous Death Valley. Arizona and the arid
regions in Mexico receive both midsummer and midwinter
rains, and the climate in these districts is such that a large
number of plant species are active in growth in both
seasons. Rain falls during February and March and
again during July and August, wetting the soil thoroughly
and thus providing water which may be taken up by the
plants. As would be expected under these conditions and
as noted above, numerous species of succulents, principally
of the cactus family, occur in these regions and form the
greater part of their flora (Plate 60). But now consider
the Mohave Desert, which also receives ample rainfall.
It lies at the same elevation above the sea as do the cactus
deserts of Arizona and Sonora, but on account of its near-
ness to the sea and the configuration of the surrounding
mountain ranges the greater part of its rainfall occurs in
the winter season, in the period of low temperatures. Only
at rare intervals do cloudbursts cause its slopes and
basins to be flooded in the warmer season. Thus the soil
is wetted only during the cold season, when the roots of
plants are inactive. With the approach of warmer weather
in March and April new absorbing rootlets are formed,
but the water content of the loose soil is then depleted at a
rapid rate by the rising temperature and by the high wind
flow of the region. Therefore only the remnant of the
winter precipitation and the uncertain and rare summer
cloudburst are available to the plants of the region, so

[277 |

DESERTS AND THEIR PLANTS

that but few succulents have been developed, among
which are a small number of species of the cactus family
(Plate 61). None of them, however, attain great size
and none are abundant.

The sap of succulents is by no means so concentrated as
that of the spiky shrubs, showing an osmotic pressure of
only three to fifteen atmospheres; but the suction power
of the plant cells is adequate to the speedy absorption of
great quantities of water within a brief period. Thus the
trunks of the massive tree cactus of Arizona, which are
one or two feet in diameter, may swell as much as an inch
in diameter during the day and night following a warm
rain at the end of the early-summer dry season. The
massive trunks of this and other types of cactus, as well
as the flattened stems of the Opuntia, can hold enough
water to meet the needs of the plant for a year or two if
no further supplies are available. Specimens of the barrel
cactus (Plate 59) have been kept on a table for five years
with the entire surface of the plant, including the roots,
exposed to the air, after which the plant has resumed
normal growth when placed with its base in the soil and
given water in the quantity and with the same frequency
to which it was accustomed before it was uprooted. The
highest observed endurance record for desert plants living
exclusively on their own accumulated water and food
material was made by the thickened tuberous base of an
Ibervillea guarequi, native to northern Sonora, which I
kept for thirteen years on a museum shelf. This plant is a
member of the gourd family; and the basal part of its
stem, which is perennial, forms a rounded mass as large
as the crown of a man’s hat. This mass is well water-
proofed, so that moisture can not escape from it, and
accumulates not only water but starch and other food
material to a bulk and weight far greater than that of the
thin stems which are sent up every year. A specimen of a
tuberous base of this kind, apparently as lifeless as a
knotty piece of wood, was placed on a shelf in a display

[ 278 ]

ADAPTATION TO DESERT CONDITIONS

case in the museum of the New York Botanical Garden
during the first half of the year 1903. During the summer
of that year a few thin green stems formed, which reached
a length of a few inches and then died without producing
flowers. This procedure was repeated the following sum-
mer and every summer thereafter until 1916. Thus the
woody tuber held enough water and food material in
storage to start its growth during thirteen seasons. If the
plant had been in the open and lying on the ground, num-
bers of small thin roots would have been sent down into
the soil and its water balance maintained by replenishing
the supply every summer. Such small roots customarily
perish at the end of the warm season; and so the traveler
may find the storage tubers only slightly embedded in the
soil, generally under trees, where they appear as lifeless
chunks of woody material except for a period of sixty to
eighty days during the season of the summer rains. The
leafy shoots developed at this time die as far back as the
basal swollen part and soon fall away.

Such are the adjustments that plants have made to the
peculiar conditions of climate and soil found in deserts.
When next we look upon a cactus we shall see back of its
pulpy stem to the solid branch whence it evolved and
know why that evolution was necessary, and back of the
bristling, close-fisted spines, with little evaporating sur-
face to the broad-surfaced leaves of plants of moister
regions. Desert plants are but another evidence of the
inexorable logic of nature.

ADAPTATION OF DeEsERT ANIMALS TO DESERT PLANTS

We may ask as a closing question how desert animals
have adapted themselves to desert plants. Much reliable
evidence is being accumulated to show that some species
of large animals in Asia, Africa, and North America may
live normally for long periods on the water contained in
the vegetation which serves as their food. Some desert
rodents are capable of existing for months on a diet of

[ 279 |

DESERTS AND THEIR PLANTS

hard seeds in which the proportion of water to dry weight
is much less than ten per cent. Many of the animals of
American deserts are known to eat the soft tissues of
cactus in which water constitutes as much as ninety-five
per cent of the total weight.

Neither man nor the horse is well adapted for life in the
desert, as both require large quantities of water daily.
Thus a man walking in the open in the deserts of Arizona,
California, or Mexico during the summer season will re-
quire from a tenth to an eighth of his total weight in water
every twenty-four hours—from sixteen to twenty pints.
A horse would use eighty to a hundred pints during the
same period. The juices of the succulent plants which
might suffice to yield an emergency supply of water to a
cow, antelope, rat, deer, or peccary generally carry bitter
substances which make them unfit for man even in the
extremity of thirst. The whitish tissues of several species
of barrel cactus, however, contain so little objectionable
material that small quantities may be taken to relieve
man’s thirst without injury. It has been found that the
Indians of southwestern North America frequently resort
to the barrel cactus to quench their thirst when on long
journeys during the hotter season of the year. The
method employed is to break open the apex of the ovoid
massive stem with a rock or remove it with a knife, then
to crush the uppermost parts of the pith and cortex by
pounding them with a rock or with the end of a heavy
stake of wood, after which the juice may be squeezed from
the mass into a vessel or into the cavity thus formed in
the stem.

The profound effect of deserts on both plant and animal
life may be readily understood when it is recalled that all
living tissue contains over ninety-nine per cent of water
and that the earliest forms of life floated in pools, were
embedded in ooze, or lay in swamps and marshes in which
there was as much water outside their protoplasm as
inside it. While plants and animals, as they have evolved

[ 280 ]

REAR Ot

, along the dry streamway of the Mohave River

al vegetation in the Mohave Desert, California

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ADAPTATION TO DESERT CONDITIONS

from their primitive forms, have appeared to move toward
all points on the horizon, one main tendency in their
migrations was obviously inevitable: Since primeval life
occupied the regions of the earth’s surface with the most
water, it could move only as it evolved, so as to occupy
the regions with less water. Certain animale including
man, might penetrate the drier regions, moving in and
out A them as their needs required; but plants, being
immobile, in order to use the deserts at all, must equip
themselves for continued existence under the arid con-
ditions. The spiky shrubs, succulent cactuses, vines with
enlarged storage roots, and all those species which suck
their nutriment from alkaline or salty soils have accom-
plished this; and so they represent the widest possible
departure from their primeval progenitors. The desert
plants have traveled farthest of all living organisms along
the road of biological adaptation. Though we may not
recognize it as such, its peculiar plant life is an element
in the fascination of the desert for us. The desert pano-
rama comprises far horizons, wind-swept dry expanses,
deeply tinted rocks and mountain ranges, blazing sunlight
and shimmering mirages, all bathed in an incessant swirl
of heat and color suggestive of an elemental and as yet
unconquered world. Into this hostile environment
armored forms of vegetation have forced their way, show-
ing by toughened leaves, indurated stems, and stored-up
water, the means by which they have gained a foothold
in a land so widely different from that of their ancestral
origin.

[ 281 |

DESERTS AND THEIR PLANTS

TABLE SHOWING RatTIo oF EVAPORATION TO RAINFALL IN THE ALGERIAN
DesErT, BY SEASONS AND STaTiIons, Durinc THE YEAR 1908, AND
AVERAGE RaTIO FOR THE YEAR BY STATIONS.!

Station Winter | Spring | Summer | Autumn |} Annual
Littoral:
INEMOUNS 205.14. 07s 2.69 | 44.09 24.1 7.4 R10
Cape Halcon.: os. B83 do Seas 58.6 16.3 BF |
Oran Nese eae BIA Ma R87, 71.0 7.95 4.2
Algiers? cots .(-ets2e 7.96 86.4 2.44 1.8
Bouzarea « o-sp,-14ah Ons St: Re 28.5 Ti45 0.93
Maison-Carrée.... RSP OHV steto) 117.4 1.48 Te
Tell (Atlas) :
Fort National ...] 0.39 | 1.4 o972 1.67 Tet
Sidi-bel-Abbés.... 793 More 38 . 3 6.0 O70
Saidasecttaaartec: te SOG u), vel. 20 B25 3-9 b.9
Batnd se wiaccusaunt Ls Qa O35 3.6 4-4
Tebessain. i072 |\ tay 4.05 88.2 28 6.0
High Plateau:
Bou Saada.... .... 5.9 7.0 76.0 Gin TINO,
Barikarras ss. cts «i 4.1 6.6 93-5 Bo. ola)
AIH Seltay cs tae Tis fool) as 67.9 18.5 ea
Geryville as cs 7.0 9.8 20.8 ga B26
Desert
Laghouat 22.6062 Gio) Blaha 2706 64.6 17.0
Ghardaialys 5. \5 en 154.9 |416.3 294.47 195.9 59-7
El Oued ai «ioc sror 68.319 5400 485.2 109.5 63.0

1 Reprinted from Cannon, W. A. “Botanical Features of the Algerian Sahara.”
Publication 178, Carnegie Institution of Washington, p. 10, 1913.

[ 282 ]

ADAPTATION TO DESERT CONDITIONS

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SELECTED BIBLIOGRAPHY

BEaDNELL, H. J. Lurwettyn. An Egyptian oasis.
London, 1909.

Brooks, Cuarites E. P. Climate through the ages.
Edinburgh, 1926

Buxton, Patrick A. Animal life in deserts. New
York, 1923:

Cannon, Wittiam A. Botanical features of the Algerian
Sahara. Carnegie Inst. Washington, 1913.

Cotvert, A. F. The exploration of Australia. London,
1896.

Dovucuty, CHartes M. Wanderings in Arabia. 2 vols.
New York, 1924.

Huntincron, Etitsworru. The climatic factor as illus-
trated in arid America. Carnegie Inst. Washington,
IgI4.

Lumuottz, Karu S. New trails in Mexico. New York,
IgI2.

MacDovcalt, Danie. T. Botanical features of North
American deserts. Carnegie Inst. Washington, 1908.

Srein, Sir M. Aurev. Ruins of desert, Cathay. 2 vols.
io pio

Part VI

THE DEPENDENCE OF PLANTS ON
RADIANT ENERGY

By
Ear S. JOHNSTON

Research Associate, Division of Radiation and Organisms
Smithsonian Institution

CHAPTER I
LIGHT AND PLANT NUTRITION

In tne Biblical account of creation light is said to have
appeared on the “first day” and the sun and moon on the
“fourth day.” Yet the “third day” saw the earth yielding
grass, herbs, and trees. Evidently the sun was not always
considered the main source of light and energy for the
earth, nor its rays a necessity to vegetation. Yet without
the sun’s radiant energy plants could not perform their
daily miracle of the conversion of minerals and other
inorganic substances into food and there would be no life
on earth. The influence of radiant energy on plants is
complex, and science has been rather tardy in inquiring
deeply into the subject, but much of interest and economic
importance has already been learned.

As a background to our discussion of some of these
things we shall need to remember that light as ordinarily
understood is limited to a very narrow band of wave-
lengths of radiant energy. The waves originate from
energy disturbances within the atom, are of different
lengths, and are transmitted through the ether. Some-
what as the number per second of air waves determines
the pitch of a sound as detected by the ear, so the length
of light waves determines color as detected by the eye.
The longer ones give us the sensation of red and the shorter
ones, of blue and violet. Certain high pitches on the
musical scale can not be detected by the human ear.
Similarly the eye fails to detect radiant energy waves
longer or shorter than those we call visible light.

The visible spectrum covers but a very small portion

[ 287 ]

DEPENDENCE OF PLANTS ON RADIATION

of the great electromagnetic spectrum. This immense
series of ether waves extends from far beyond the short
gamma waves, which are produced from radioactive sub-
stances such as radium, to the long wireless waves. In
wireless telegraphy, waves from 3 meters to 20,000 meters
in length are used; the shortest gamma rays, on the other
hand, are approximately one-trillionth of a meter in
length. If this range of wave-lengths found in the great
electromagnetic spectrum were represented on a key
board 2,300 miles long—the air-line distance from Wash-
ington to Los Angeles—then the part covered by the
visible spectrum would be an extremely small fraction of
an inch in length. Beyond the small visible spectrum, on
one side, are the u!tra-violet rays, the R6ntgen or X-rays,
the gamma rays, and the cosmic rays; on the other side
are the infra-red rays, the so-called heat rays, Hertzian
waves, and the long wireless waves.

In addition to the wave-length of light (perhaps rather
than /ight the term radiant energy should be used), there
are two other factors to be taken into account when con-
sidering the relation of plants to radiant energy. One of
these is the intensity of the energy; the other is the length
of time the plant is exposed to a given radiation. All three
of these factors, duration, intensity, and wave-length—
sometimes spoken of as qualityhave been given con-
siderable study by chemists, physicists, and plant physi-
ologists.

Not all plants are directly dependent on radiation, for
not all plants manufacture their own food. Those that
do not are the saprophytes, which feed on dead or decaying
organic matter, and the parasites, which grow and feed
on the body tissues of other plants or animals. Neither
type needs light, and so we find saprophytic mushrooms
and toadstools thriving in dark caves, and parasitic bac-
teria in darkness within the body of man and other ani-
mals. All these plants lack the green coloring matter,
chlorophyll, which with the aid of sunlight enables plants

[ 288 |

PLATE 63

00
150.
400

650

Chlorophyll a

OO =
650
600
550
+00

Chlorophyll b

Absorption spectra of the two chlorophylls The successive horizontal

bands represent a series of spectra of light after passing through

solutions of increasing depth. The red, or longer, wave-lengths are

on the left; the violet, or shorter, wave-lengths on the right. After
Willstatter and Stoll

LIGHT AND PLANT NUTRITION

to manufacture food out of inorganic matter, water, and
carbon dioxide. It is the green, or chlorophyll-bearing
plants in which we are interested here.

LicHT AND PHOTOSYNTHESIS

Man, like all other animals, secures from his food
enough energy and the necessary building material for
growth, reproduction, and other life processes. The
foods essential to the supplying of these requisites are
carbohydrates, proteins, and fats. Green plants obtain
the same things from similar foods. But they do one
thing more, which they alone of all living organisms can
do—they manufacture their own food. The manufacture
of carbohydrates (sugars and starch) by green plants is
called photosynthesis—putting together by light. Let us
see what is known of this unique and fundamental manu-
facturing process.

There may be and probably are numerous other photo-
chemical reactions going on in plants, but photosynthesis
refers exclusively to the building up of carbohydrates. The
process has also been termed carbon assimilation because
of the large amount of carbon dioxide (CO») absorbed in
its accomplishment. The exact chemical reactions that
take place during photosynthesis are not fully understood
in every detail. We do know that the raw materials
needed are carbon dioxide and water; that light and
chlorophyll and proper temperature conditions (usually
from 32° to 115° F.) are essential to the process. Beyond
these temperature limits photosynthesis ceases or goes
on very slowly. We know, also, that one of the sal
products formed is grape sugar, or glucose (CoH Og).
The chemist’s shorthand system for representing this
reaction 1s:

6 CO, +6 H.O +light = C.H 1.20. +6 O,

Evidently chlorophyll does not enter the reaction as a raw
material or as a by-product. It apparently acts as a

[ 289 |

DEPENDENCE OF PLANTS ON RADIATION

catalyzer; that is, it effects the rate of a chemical reaction
yet itself remains unchanged.!

The nature of chlorophyll was but vaguely understood
until a few years ago when two German scientists, Will-
statter and Stoll, greatly increased our knowledge by
their brilliant research work. Chlorophyll 1s composed
of two separate pigments made up of carbon, hydrogen,
oxygen, nitrogen, and magnesium in the following pro-
portions:

Chlorophyll 2 C;;H72.0;N.sMg
Chlorophyll b C5sH7006N «Mg

Chlorophyll @ constitutes about seventy-two per cent of
the total green pigment and chlorophyll 4 the remaining
twenty-eight per cent. Although the presence of iron
(Fe) is necessary for the formation of chlorophyll it does
not occur in the molecule of either pigment. Lack of iron
results in a pale or yellow plant, a condition which has
been corrected in young conifer trees and in pineapple
plants by spraying them with solutions of iron salts.
Now, to consider the relationship of radiation to photo-
synthesis, we find that the strength, or intensity, of light
required for the process varies somewhat with the plant:
some work under the high light intensities found on the
deserts of southwestern United States; others thrive best
in the subdued light of a dense forest floor. One curious
little moss (Schistostega osmundacea) grows in caves, where
light is very much reduced. It is equipped with a plate

1Dr. William F. G. Swann, of Philadelphia, is responsible for an amusing illustration
of the property of a catalyzer. His story runs as follows:

A certain Arab of property, dying, left his estate in this curious manner: one-half to
his eldest son, one-third to his second son, and one-ninth to his youngest son. The
executors, however, were somewhat embarrassed to find that the estate comprised
seventeen camels, a number divisible neither by two, three or nine. In this quandary
they appealed to the Sheik. The latter said:

“While compared to our deceased brother I am but a poor man, yet in my great
concern to promote his dying intent I will even add one of my camels to his estate.
Then the eldest son shall have one-half of eighteen or nine camels, which is more than
our brother intended; the second shall have six camels, and the youngest, two, still in
each case more than our brother intended. And now behold the blessing of Allah on
generosity! For lo! nine camels and six camels and two camels make altogether but
seventeen camels, and my camel returns to me.”

[ 290 ]

LIGHT AND PLANT NUTRITION

of cells forming a battery of lenses capable of focusing
the scattered light on its chlorophyll-bearing bodies
(chloroplasts) and is thereby provided with a means of
carrying on photosyn-
thesis in very dimly
lighted corners of the
earth.

Plants display nu-
merous adaptations for
adjusting themselves
to various light inten-
sities. The English ivy
(Hedera helix), for in-
stance, arranges its
leaves in a _ mosaic
pattern that exposes
the greatest area to
chev Might “On -the
other hand, the com-
pass plant (S7/phium
laciniatum) and the
wild lettuce (Lactuca
scariola) turn the edges
of their leaves in a
general _ north-south
direction. Thus in the
morning and the even- Fic. 51. Cross section of a leaf,
ning when the light showing position of chlorophyll
intensity is weakest, bodies (a) in diffused light and (b)

in intense light. Arrows indicate
the flat surfaces of direction whence light is coming.
their leaves are in a Aftee Stahl

position to receive the

maximum amount of light, whereas at noon, when the light
is strongest, the edges are turned toward the sun. Even the
shape and arrangement of the cells containing the chloro-
plasts are such that the amount of chlorophyll exposed to
the light can be varied, as illustrated in Figure 51.

[ 291 ]

DEPENDENCE OF PLANTS ON RADIATION

The intensity of sunlight varies under natural condi-
tions from o at night to 10,000 foot-candles at brightest
noonday. A foot-candle is the intensity of light from a
“standard candle” at the distance of one foot. Most
plants need far less light than maximum sunlight in-
tensity for photosynthesis. In recent years some very
interesting results have been obtained by growing plants
in the artificial light of Mazda electric lamps. For in-
stance, plants quite normal to all appearances have been
grown under intensities as low as 2,000 to 3,000 foot-
candles. Photosynthesis frequently goes on even at
much lower intensities.

The wave-length, or color, of light also plays a determ1-
nant part in photosynthesis. If a beam of white light 1s
passed through a prism, it is broken up into a series of
colored lights called the spectrum. These colors corre-
spond to energy waves of different lengths. The wave-
lengths of representative colors are approximately as
follows:

Red 0.650 micron?

Orange 0.600 i
Yellow 0.580
Green } (0.520
Blue 0.470
Violet 0.410 if

Anyone who has seen a rainbow or the spectrum knows
that one color merges gradually into another. Ifa green
leaf or an alcoholic solution of chlorophyll be placed in the
beam of a white light before it enters the prism the spec-
trum will look quite different. One heavy dark area will
blot out a considerable portion of the red light and an-
other will remove a wide area of light in the blue and
violet (Plate 63). This means that the chlorophyll has
the power to absorb a portion of the red light and most of
the blue and violet.

1 Micron is a measure of length and is equal to 0.001 millimeter or 0.cocooI meter.

[ 292 |

LIGHT AND PLANT NUTRITION

Not all wave-lengths, or colors, are of equal importance
in photosynthesis. This can be shown by spreading light
through a prism on a leaf previously kept in the dark and
carefully noting the portions of the leaf covered by the
various colors. If the leaf is then bleached with alcohol
and stained with iodine the portions illuminated by the
red, blue, and violet lights will be stained blue or black,
indicating the presence of the carbohydrate, starch. The
inevitable deduction is that wave-lengths corresponding
to portions of the red, blue, and violet are more effective
in photosynthesis than the others. Specifically, radiant
energy corresponding approximately to wave-lengths
running from 0.640 to 0.680 micron in the red, and from
0.475 micron in the blue to the end of the visible spectrum
are very important energy sources in the production of
carbohydrates by the chlorophyll.

How efficient is this plant food factory in its utilization
of solar energy? Two English scientists, Brown and
Escombe, made a very interesting study in which they
measured the amounts of energy received by the leaf and
then attempted to account for its distribution and use.
Considering all the energy received as I00 per cent, its
utilization in one example may be expressed as follows:

Per cent Per cent
Energy used im photosynthesis.............2..) 0.66
Energy used in evaporating water from the leaves
EGA NS Pita ClO)! atiac wiser. a¢s).alesig sie jeceiue ais oe 48 .39

Total-energy expended in work...) 450251. 0% <6: 49.05
Energy transmitted (radiant energy passing

Piimougla leat) canvas ate ooh AN ONE Bi iu 9h 31.40
Energy lost by heat conduction to the surroundings 19.55

Total energy not used by leaf for work.......... 50.95

Total energy to be accounted for............... 100.00

Recently Professor Shull, of the University of Chicago,
has pointed out that another important loss of energy

h2o8)|

DEPENDENCE OF PLANTS ON RADIATION

from a leaf is that by reflection. In his own experiments
he found that the darkest-green leaves lost by reflection
as much as six to eight per cent of the light falling upon
them, and the lightest-green leaves lost twenty to twenty-
five per cent.

Energy is usually measured in terms of heat, because all
forms of energy can be reduced to heat. Energy of
motion, such as that of a moving automobile, can be re-
duced to heat by applying the brakes and measured by
noting the heat given off from the brake drums; electrical
energy may be passed through a small wire and the rise in
temperature of the wire observed; energy of sunlight
that fell on the earth ages ago and was stored in the form
of coal may easily be converted to heat by burning the
coal; even the energy of our daily bread has been calcu-
lated in terms of heat, and it is now quite easy to deter-
mine from prepared tables how much of each food must
be eaten per day to give our bodies the proper amount of
energy for the type of work we do. The unit of heat
energy used by scientists is the calorie. It represents the
amount of heat required to raise the temperature of a
gram of distilled water from 15° to 16° centigrade.

Professor Transeau of Ohio has made some interesting
calculations on the energy budget of a hypothetical acre
of corn (10,000 plants) based on growth from June 1 to
September 8 (100 days). The following is the summary
of the budget.

Calories Calories
Totalvenergy available.:. 27.) 2 does 2,04 3,000,000
Energy used in photosynthesis.......... 33,000,000
Energy used in transpiration............ 910,000,000
‘Total energy comsumied .))2)30)o)5:)ncuve\e «\aie 943,000,000
Energy not directly used by the plants.... I, 100,000,000

(Energy released by respiration, 8,000,000 calories.)

A study of these figures indicates that the plant uses
about forty-six per cent of the available energy, and the
environment takes up fifty-four per cent. Some of the

[ 294 |

PLATE 64

ie e
ae
J 5 ?

Healthy tomatoes on plants grown in water cultures. The roots
absorbed the necessary mineral elements from a watery solution and
were never in contact with soil

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LIGHT AND PLANT NUTRITION

interesting generalizations which he makes from his cal-
culations are that:

An acre of 100-bushel corn uses during the growing season about
408,000 gallons of water or 15 acre-inches.
The evaporation of this water consumes about 45 per cent of the

available light energy.
In photosynthesis the corn plant utilizes about 1.6 per cent of the

energy available.
An acre of 1o0-bushel corn manufactures on the average 200 pounds

of sugar a day.

Of the sugar manufactured nearly one-fourth is oxidized in respira-
tion.

At maturity the grain contains about one-fourth of the total energy
utilized in photosynthesis, or about 0.5 per cent of the energy available.

One fact stands out above all others in studies made
on the energy budget of plants, and that is that plants are
very low in efficiency. It is certain that a man-made
machine as low in efficiency as is the green plant would
not be tolerated in the present age of mass production and
its concomitants. However, since man is still unable to
do the work of a plant he is hardly in a position to give
adverse criticism.

THe INFLUENCE OF LIGHT ON THE ABSORPTION OF
ELEMENTS OTHER THAN CARBON

Photosynthesis, as we have said, refers only to the
building up of carbohydrates by the green plant. From
the simple sugar, glucose, which is an early product of
photosynthesis, other carbohydrates are built up. Such
substances as starch, cane sugar, and cellulose, or wood,
have the same elements as glucose but in slightly different
amounts and proportions. How does the plant get its
other foods, such as proteins and fats? Apparently they
are built up from carbohydrates and certain inorganic
elements absorbed from the soil, including principally
nitrogen, phosphorus, potassium, line sulphur, and
magnesium; these are the elements found in the common
fertilizers used by the farmer. By properly uniting the

[ 295 ]

DEPENDENCE OF PLANTS ON RADIATION

atoms of these elements with the carbohydrate com-
pounds the green plant is able to form the organic foods
essential to all life.

This discovery of the use by plants of inorganic sub-
stances as food material is relatively recent. In ancient
times men believed that plant food consisted entirely of
decayed animal and plant remains—a belief based prob-
ably on the theory that organic matter could originate only
from other organic matter. But in the year 1699 experi-
menters began to grow plants with their roots in pure water
and in water containing small amounts of dissolved matter,
and in 1840, Liebig, the famous German chemist, made
the bold announcement that the food material of plants
is not decayed organic matter, but inorganic substances
such as nitrogen, phosphate, and potash. Since Liebig’s
time many experiments have been conducted in the
growing of plants in water containing a great variety of
dissolved minerals, and much exact knowledge has been
gained regarding plant-food materials. Plate 64 shows how
successfully tomato plants can be grown in water cul-
tures. Work of this nature has a direct practical bearing
on fertilizer practices, for unless one knows what a plant
requires for its growth, both time and money may be lost
in feeding it useless material.

We have so far mentioned the elements carbon, hydro-
gen, oxygen, phosphorus, potassium, nitrogen, sulphur,
calcium, iron, and magnesium as essential to plant growth.
The omission of any one of them from the plant’s diet
will bring about a serious distortion of growth followed
by death. For example, plants suffering from a deficiency
of phosphorus will turn a dark green or purple and even-
tually die; without calcium the growing points of the
stems die in a very few days; a lack of nitrogen or of iron
will cause the plant to turn a pale green or yellow; a
deficiency of potassium is frequently indicated by the
appearance of tiny spots or dead areas on the leaves

(Plate 65).
[ 296 |

LIGHT AND PLANT NUTRITION

To this list of essential elements several others have
been added in recent years. With improved technique and
the use of highly refined chemicals it has been found that
plants will not grow normally unless they are given ex-
ceedingly small amounts of certain substances like zinc,
manganese, and boron, which, in larger quantities, would
be very poisonous. A tomato plant, to take a specific
example, will fail to grow in a solution lacking boron,
which is the element found in ordinary boric acid. If,
however, one part of boron is added to two million parts
of the solution bathing the plant roots, the resulting
growth is amazing. Two tomato plants are illustrated in
Plate 66. The solutions in which these plants were grown
were exactly alike with the exception that to the one on
the right this small trace of boron was added in the form
of boric acid.

How plant roots absorb these inorganic substances has
provoked much controversy among investigators. It is
certain that very small particles of these elements (ions
and perhaps even molecules) often enter by a process
called diffusion. A little ink dropped into a glass of water
will spread to all parts of the water and finally become
equally dilute at every point; this is diffusion and results
from the fact that the general movement of particles is
from a concentrated to a dilute condition. In a somewhat
similar manner particles of calcium, potassium, and other
inorganic elements diffuse from the watery solution in the
soil into the watery interior of plant cells. The process
differs, however, from that of the ink in a glass of water.
Plant cells are surrounded by membranes which, under
certain conditions, make the passage of many small par-
ticles exceedingly difficult, even though there is a con-
tinuous waterway connecting the outside with the inside.
These plant membranes are very sensitive in their be-
havior and react to changes in temperature, light, chemical
surroundings, and electrical conditions. The entrance of
the various elements is not controlled by the rate at

[ 297 ]

DEPENDENCE OF PLANTS ON RADIATION

which water is drawn into the cells, but depends largely
on the properties of the membranes and cell sap. Water
may enter at one rate while the inorganic elements move
in or out at other rates, somewhat like ships entering or
leaving a harbor independently of the direction of the
tide.

It frequently happens that a given element accumulates
in a cell so that there are more of its particles per unit
volume in the cell than outside. Here the movement can
not be explained by diffusion alone for if that were the
entire story the particles would be moving out. It seems
evident that light in some manner not yet fully under-
stood influences this movement. Perhaps it brings about
changes in the cell sap or in the cell membranes them-
selves. Sir E. J. Russell, the director of the famous
Rothamsted Experimental Station in England, points out
that “tomatoes respond better to nitrogenous fertilizers
in a sunny than in a dull, cold season, but better to
potassic fertilizers in a dull, cold season than in a sunny
one.”

To study the fundamental processes of absorption of
mineral elements by plants was the primary object of
a number of interesting experiments carried out by
Prof. D. R. Hoagland and his associates at the University
of California. Nite//a, a water plant, was selected for this
work because of the large size of its cells (they vary from
a half inch to three inches in length). When these cells
are punctured it 1s comparatively easy to squeeze out
the cell’ sap without contaminating it with crushed cell
walls and other cell structures. The chemical element
chosen for the experiment was bromine, because in low
concentrations it is practically nontoxic to plant cells and
because it is not normally found in the sap of these plants.
The plants were grown in a nutrient solution to which 4
very small amount of the element bromine was added.
Some plants were kept in the dark while others were ex-
posed to light. When the sap was squeezed out and

[ 298 |

PLATE 66

Tomato plants grown in similar solutions except that in the solution of
the plant on the right one part of boron was added to two million
parts of water

PLATE 67

-—- TEMPERATURE }

HUMIDITY

The influence of light on the opening and closing of stomata as illus-

trated by the reactions of stomata of an onion leaf during a twenty-

four-hour day (x 240). After Loftfield; courtesy of the Carnegie In-
stitution of Washington

LIGHT AND PLANT NUTRITION

analyzed, it was found that sap taken from the illumi-
nated cells contained as much as four times the amount
of bromine contained in the sap from the cells kept in
darkness. The concentration of bromine in the sap of
this second group of cells did not become greater than
that in the solution surrounding the cells. On the other
hand the bromine in the sap of the illuminated cells
reached a much higher concentration than that of the
medium in which they were growing. It was also found
that doubling the light intensity increased the absorption
of bromine thirty per cent.

Professor Hoagland’s own words summarize this dis-
cussion very well. “All the evidence now available shows
that it is possible for certain inorganic elements to be
taken out of a dilute solution and stored in a solution of
much higher concentration inside the cell. . . . Light ob-
viously contributes energy toasystem, and it would seem
necessary to assume that this energy, which, under ap-
propriate conditions can be stored, may be utilized to
bring about a movement of solutes [dissolved mineral
elements] from a region of low concentration to one of
higher concentration.” There is evidence on record that
the absorption of the essential elements is likewise in-
fluenced by light, but the exact relationship is an im-
portant problem yet to be solved.

Although plants secure mineral elements from the soil,
very important building blocks for the complex foods
manufactured by them come from the air. As mentioned
earlier, carbon dioxide enters the plant from the air. On
the under side of many leaves are tiny openings through
which this gas enters into the spacious interior where
it is absorbed by the moist cell walls abutting on those
wonderful corridors. From the surfaces of these cells the
carbon dioxide gas, in the form of a solution, is taken into
the cells and manufactured into the carbohydrates—
sugar and starch.

The architecture of this portion of a leaf is a beautiful

| 299 |

DEPENDENCE OF PLANTS ON RADIATION

example of the economy of nature. Carbon dioxide is very
soluble in water so that it is to the plant’s advantage to
expose a large moist surface for its absorption. But a large
moist surface exposed directly to the air would result in
an enormous loss of water from the plant, cutting down
growth and resulting in other injuries. For structure of
leaf see Part I, page 24. For this reason the surfaces
of leaves are covered with layers of epidermal cells usually
so constructed that very little water can evaporate from
them. A microscope will show us how the plant has got
around the problem of obtaining carbon dioxide without
undue loss of moisture. Large areas of moist cells are ex-
posed to the atmosphere of numerous passageways called
intercellular spaces. These passageways open to the
exterior world through tiny ventilators called stomata.
Each stoma is protected by two crescent-shaped cells, the
guard cells, which open and close it as conditions require.
When the guard cells are supplied with a sufficient amount
of water, it has been discovered that they open the tiny
ventilators in the presence of light and close them in the
dark. In Plate 67 the position of the guard cells and the
size of the tiny openings are shown for different hours of
the day and night. This seems to be logical, for the
chlorophyll is actively engaged in the process of making
carbohydrates during the period of light and large quan-
tities of carbon dioxide are then needed. At night the
factory shuts down and closes its flues. It 1s thus seen
that light is an extremely important factor in assisting the
plant to obtain its raw material for the manufacture of
sugar and starch as well as a requisite for the process
itself.

| 300 |

CHAPTER II
LIGHT AND GROWTH

Pianrs growing under the natural conditions of the out-of-
doors are constantly submitted to enormous changes of
light intensity. In the temperate zones this intensity
changes from zero at night to as much as 10,000 candle-
power at noon in clear weather and back again every
twenty-four hours. Passing clouds, the presence of dust
particles in the atmosphere, and even changes in the sun
itself may alter the intensity of light during the day or for
several days. In addition to these daily changes there are
seasonal changes such as that occasioned by the fact that
sunlight in the northern hemisphere is more intense in
summer than in spring or autumn. Plants must be cap-
able of adjusting themselves to all such daily and seasonal
changes of light intensity.

The importance of the intensity of sunlight in photo-
synthesis has already been mentioned. To a large extent
this factor determines also the type of plant growth. In
darkness plant stems grow much longer than they do in
light, while prolonged darkness will produce long inter-
nodes in many plants and check leaf growth almost com-
pletely. Under proper light conditions these same plants
would have short stems and well developed leaves.
Leaves grown in bright sunlight show marked differences
in structure from those grown in dim light. Shaded leaves
are thinner and contain poorly developed palisade tissue.
Even the shape of leaves on the same plant may be altered
by shading. The bluebell (Campanula rotundifolia) de-

velops two kinds of leaves. The basal ones are round

[ 301 |

DEPENDENCE OF PLANTS ON RADIATION

or heart-shaped and for the most part toothed around the
edge and have long petioles. The stem leaves, which
develop later under better light conditions, are narrowly
lanceolate, smooth edged, and have shorter petioles.
Properly shaded, this plant will develop long-petiolated
leaves on its upper part similar to the basal ones.

In view of the immense changes that occur in the in-
tensity of sunlight, one may wonder what intensity best
suits the needs of plants. Of course, plants differ greatly
in this respect and some will grow under light conditions
which would be fatal to others. The Boyce Thompson
Institute for Plant Research has made a number of in-
teresting measurements of tomato, tobacco, and buck-
wheat plants grown out-of-doors under cloth shades of
different thicknesses. The plants were uniformly venti-
lated and other conditions were made as nearly equal as
possible. One shade cut out eighty per cent of full day-
light, another, fifty-three per cent, a third, only twenty-
six per cent. A fourth group of plants was grown without
any shade. When these plants were dried and weighed, it
was found that a reduction of one-half full daylight in
midsummer made little difference in the weights; but
from August 10 to September 30, when the light was
weaker, all degrees of shading retarded growth. The
Boyce Thompson Institute also found in other experi-
ments that a number of plants were just able to sur-
vive at the very low light intensity of forty foot-candles.
This, of course, is too low for good growth. Doctor
Shirley states: “Low light intensities tend to produce
vegetative growth at the expense of flowers and fruit,
top growth at the expense of root growth, large leaf
areas at the expense of leaf thickness, and succulence at
the expense of sturdiness.”

A second factor that greatly influences plant growth is
the duration of light. North of the equator there are
in summer more hours of sunlight than of darkness; in
winter the reverse is true. During the northern growing

[ 302 ]

LIGHT AND GROWTH

season the duration of daylight near the pole is twice
that near the equator, and there are corresponding dif-
ferences for localities between these extremes. On the
other hand, the light intensity increases tenfold pro-
gressively from the pole to the equator. Duration of light
is a factor in plant growth that man has but recently
begun to appreciate; by artificially lengthening or shorten-
ing the daily light period the type of growth can be con-
trolled to an extraordinary degree.

The term photoperiodism has been used by Garner and
Allard, of the United States Department of Agriculture,
to designate the response of plants to the length of day-
light. Numerous experiments which they have carried
out demonstrate conclusively that ey plants “‘attain
the flowering and fruiting stages only when the length of
day falls within certain limits, so that in such cases Hower-
ing and fruiting occur only at certain seasons of the year.

. It was discovered, also, that exposure to a daily light
period intermediate between that favorable only to vegeta-
tive development, on the one hand, and that favoring
only flowering and fruiting, on the other hand, tends to
cause both forms of activity to progress simultaneously.
This combined form of activity constitutes what is com-
monly known as the ‘everflowering’ or ‘everbearing’
behavior.” The length of the light periods was controlled
by placing the plants in and out of darkened sheds. In
some experiments the period of light was lengthened by
exposing the plants to Mazda electric lamps.

One set of the Garner and Allard experiments illustrates
the curious localization of the response in plants to the
relative length of light and dark periods. Yellow cosmos
plants were used. The arrangement of the apparatus was
such that the tops of some plants were grown in light-
proof compartments which were opened for ten hours
each day, while the lower portions were exposed to the
full length of daylight. Flowers promptly appeared on the
upper parts of these plants, whereas the lower portions

[ 303 |

DEPENDENCE OF PLANTS ON RADIATION

continued to grow without flowering. The upper and
lower portions of other plants were treated similarly but
in a reverse manner. Under these conditions the upper
portions grew vegetatively, while the lower halves flow-
ered. In still other experiments the middle section of the
plant was exposed to long daylight periods, while the
upper and lower portions were given short exposures.
The result was that flowers appeared on the upper and
lower sections but the middle section continued in the
vegetative stage. Thus the length of the lighting period
appears to bring about in the same plant a localized re-
sponse in much the same manner as it would in separate
plants of the same species.

Several years ago a new kind of tobacco was found
growing in southern Maryland. It produces many leaves
per plant and has become important economically. This
Mammoth tobacco (Plate 68), as it has been named,
usually does not flower and set seed under field conditions
in Maryland. The periods of daylight are too long during
the summer, and when the days become short enough for
flower production the temperature is too low. If, how-
ever, the plant is grown in the winter in greenhouses or is
grown further south, it will produce flowers and seeds.
On the other hand, if the short daylight periods of winter
are supplemented by artificial light in the greenhouse,
flowers will not form (Plate 69).

The third light variable affecting plant growth is wave-
length, about which something has already been said.
One naturally thinks of sunlight as white light. In reality
white light is a mixture of colors. That is, it is composed
of a large number of radiant energy waves of different
lengths. Years ago Sir Isaac Newton demonstrated the
composition of white light by passing a beam of it through
a prism. The separate colors of the spectrum were then
reflected from small mirrors to one point, thus combining
them again into white light. Sunlight is composed of the
colors of the rainbow in such a manner that it usually

[ 304 ]

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69 ALVId

LIGHT AND GROWTH

looks white at noontime. By means of a spectrobolometer,
an instrument for measuring the intensity of different
light waves, it is found that the color composition of sun-
light changes greatly from noon to sunset. At noon, the
sunlight coming through the earth’s atmosphere is more
intense in blue, but as the sun sinks the red becomes pre-
dominant. On clear evenings this color change can be
detected by the eye. Light comes through so great a
thickness of atmosphere in the evening that the less
transmissible colors—violet, blue, and green—are reduced,
leaving the red preponderant. Change of season also
produces a change in the color composition of daylight.
Evidently, therefore, plants depending directly on the
sun for their supply of energy are compelled by nature
to grow under constantly changing conditions of color as
well as of intensity and duration of light.

It is a common observation that stems of many plants
grow more rapidly at night than in daylight. White
light actually appears to retard stem growth; so do the
different colors of which it is composed, though each does
so to a different degree. The short wave-lengths at the
violet end of the spectrum have the greatest retarding
effect, the longer green and red waves have less effect.
In general, plants will grow tall under red glass and re-
main short under blue and violet glass. Furthermore,
chlorophyll development—that is, the amount of green
pigment formed in the plant—will be more rapid in red
light than in blue or violet light. It is thus seen that
although a definite range of wave-lengths is beneficial
for one plant function such as growth in length, it may
be superfluous or even detrimental for another function
such as the manufacture of chlorophyll.

Flowers exposed to sunlight from which the short wave-
lengths have been removed will become paler. The
brilliant colors of Alpine flowers are attributed to the
presence of light of short wave-lengths found at the high
altitudes in Switzerland and in the Rocky Mountain

[ 305 |

DEPENDENCE OF PLANTS ON RADIATION

regions of America. Plants transplanted from these high
altitudes to the plains below lose some of their brilliant
coloring, a phenomenon explained by the fact that light
of short wave-lengths is cut out by the denser atmosphere.

The Boyce Thompson Institute for Plant Research has
built a series of greenhouses, using special glass which
transmits light of rather restricted wave-length ranges.
Experiments in them have shown that the blue and violet
end of the spectrum can not be eliminated from sunlight
without impairing the growth and vigor of the plants.
Plants grown in greenhouses from which the blue and
violet light waves were cut out grew taller and had thinner
stems and fewer branches; also the cells of their stem
and leaf tissues were thin walled and held together less
compactly than in normal plants. These same plants
showed good chlorophyll production, but a decrease in the
amount of carbohydrates, and considerable delay in time
of flowering.

Light is clearly one of the important factors controlling
plant growth. Its effects are direct, as shown in the pre-
ceding pages, and indirect, through its influence on climate.

[ 306 ]

CHAPTER III
PHOTOTROPISM

Ir we examine the ivy covering the wall of an old house we
will find myriads of tiny stalks growing out away from the
wall. These stalks, or petioles, supporting the expanded
leaves, suggest small arms outstretched and extending
the palms of as many hands to the world for assistance.
In reality that is just what is taking place. The ivy plant
needs light to run its carbohydrate factory. The petioles
of the leaves grow out toward the light while the broad
expanded portions of the leaves set themselves at right
angles to the light rays, so as to use to best advantage
the light coming within their reach. A potted plant like the
geranium will grow symmetrically in a greenhouse where
light is of uniform brightness on all sides. If, however, it
be placed by the window of a living room where light is
much brighter on one side than on the other, it will turn
its leaves toward the window and resemble the ivy in its
growth habit of turning toward the light. Physiologists
apply the term phototropism to this type of growth.
Plants very easily grow lopsided when exposed to light
that is more intense on one side than on the other. If the
plant by the window were slowly and continuously turned
it would grow symmetrically like the one in the green-
house, for each part of the plant would receive an equal
amount of light and so grow uniformly.

Some parts of plants, such as leaf petioles and young
shoots, grow toward the light, and are positively photo-
tropic. Other parts grow away from the light and are
negatively phototropic, whereas those like the expanded

[ 397 ]

DEPENDENCE OF PLANTS ON RADIATION

portions of leaves, that grow across the beam of light, are
transversely phototropic. The roots of most plants are
relatively unresponsive to light. There are, however, a
few plants—such as the mustard and radish—whose roots
show negative phototropism. Plate 70 shows a white
mustard seedling growing through a tiny hole in the center
of a glass dish, with the root extending into a beaker of
nutrient solution. The source of light for this plant was a
200-watt electric lamp placed about two feet away and
so fixed that the light came to the plant from the direction
indicated by the arrow. Note that the small leaves have
already started to expand at right angles to the path of
light, thus showing their transverse phototropic ten-
dencies, while the stem and root show respectively posi-
tive and negative responses.

Although it is perfectly clear that a plant profits greatly
by facing its leaves toward the light, it is difficult to be-
lieve that it is conscious of what it wants and acts ac-
cordingly. To be correct in this materialistic age, all
such actions should be explained on a physical or chemical
basis. Accordingly we may ask, what are the mechanics
of phototropic bending?

To go back to some of the earlier explanations, about
one hundred years ago De Candolle, the Swiss physician
and botanist, thought that positive phototropic bending
was due to the retarding effect of light on growth. The
side of the stem most brightly illuminated would grow
more slowly and so bring about a bending toward the light
source. The remarkable elongation of potato sprouts
in a darkened cellar would seem to substantiate the view
that plant stems grow longer in the dark than in the light.
Thus it seems logical to deduce that the shaded side of
the stem of the geranium plant growing at a window
would elongate more than the side receiving more light,
and thus cause the stem and the petioles to bend toward
the window. De Candolle’s theory is further supported
by the fact that mature plant tissues that have almost

[ 308 ]

PLATE 70

The reaction of parts of a mustard seedling to light. Stem bends
toward, roots away from the light, and leaf places itself at right angles
to the light

PHOTOTROPISM

completed their growth cycle do not show this bending
nearly so much as young tissues. Only the tissues that
contain cells still capable of dividing or of enlarging are
capable of exhibiting this phenomenon.

But objections came to be made to this early view of
phototropism. Such distinguished men as Darwin and
Pfeffer, the German plant physiologist, were led to be-

Fic. 52. Diagrammatic representation of photo-

tropic bending of coleoptiles at their bases when the

tips are illuminated from one side as indicated by

arrows. The tip on the right has been cut off and
attached with gelatin

lieve there existed a region in the plant capable of receiving
a stimulus and that such a region was more or less local-
ized. In one experiment the apex of a young sprout was
exposed to light, but the bending occurred at the base,
which was not illuminated (Fig. 52, left). It thus ap-
peared that in addition to a region of perception, there is
a region of response. If this is true, then the tissues be-
tween these two regions must be capable of conducting
the excitation from the former place to the latter. This
suggests on the face of it that a plant is very much like an
animal, which, for example, sees food with its eyes. The

[ 309 |

DEPENDENCE OF PLANTS ON RADIATION

excitation travels over the nerves to the legs which react
in such a manner as to carry it toward the food. In a
growing shoot, the tip perceives light on one side. The
sensation is transmitted to the part lower down where
differential growth goes on in such a manner as to point
the stem or shoot toward the light. But this is accrediting
the plant with a reflex nervous system which it does not
have.

A good deal of work on phototropism has been done
with the coleoptiles of plants belonging to the grass
family, particularly the oat. The coleoptile is a leaf
sheath surrounding the bud of the ascending foliage leaf.
As recently as IgIO one ingenious experimenter hit upon
the idea of cutting off the top of a coleoptile and sticking
it back on the stub with melted gelatin. When the tip
was illuminated on one side the shoot still showed marked
phototropic bending at the base (Fig. 52, right). Did the
stimulus received by the tip travel to the base after passing
through a layer of gelatin? Further interesting experi-
ments are reported in which the “heads” of coleoptiles
illuminated from one side were cut off and stuck on the
stumps of decapitated coleoptiles grown in the dark.
These ‘“‘doctored up” coleoptiles when allowed to continue
their growth in the dark showed positive phototropic
curvatures in the proper direction.

Still other theories have been suggested to account for
the phototropic bending of coleoptiles. Certain experi-
ments would indicate the presence of growth-accelerating
substances in the tips of growing stems. The phototropic
curvatures depend upon the way these substances travel
through the stems and this in turn is governed by light.
It is further claimed that some of these substances have
been extracted from the coleoptile tips and used to induce
in other seedlings certain phototropic-growth responses
independent of light. Some extremely interesting work
has also been done in Holland by Professor Went and his
students. Accounts of their investigations should be

[ 310]

PHOTOTROPISM

consulted by those interested in going deeper into the
subject of phototropism.

Professor Priestley of England has recently been study-
ing these very fascinating plant traits and has done much
toward giving this peculiar phenomenon a rational ex-
planation. He shows that phototropic curvature in
coleoptiles is consistent with De Candolle’s hypothesis of
the retarding effect of light on growth in spite of many
seemingly discrepant experiments.

To understand what takes place, we must consider a
few essential conditions of growth in plants. Plant tissue
that is capable of growth by active cell division is called
the meristem tissue. To permit of meristem growth water
and food are necessary. Plant stems have tiny tubes
extending up and down through which water and solu-
tions of food material may pass. In order for these ma-
terials to reach the cells located at a distance from the
main-trunk service tubes, they must pass through the
walls of the intervening cells. The more permeable these
walls are to water and the foods dissolved therein, the
better are the chances for rapid growth of the meriste-
matic tissues. Cells stop growing when they lose water
faster than they can absorb it or when they can not get a
sufficient amount because of a blockade in the line of cell
walls connecting them to the water mains (vascular tissue).
The entire system is very delicately balanced.

How then is this sap, or water, system related to
phototropic bending? As Professor Priestley states, “In
this delicately balanced equilibrium, strong lateral illumi-
nation may mean that the sap supply first fails on the side
more directly lit, where evaporation will more rapidly
bring about a state of ‘incipient drying’ in the walls of the
tissues. . . . If the walls between the vascular supply and
superficial meristem are in this condition, food supplies
to the meristem will fail, and there will be a cessation of
meristematic growth.” That is, less growth will occur on
the drier or more illuminated side because the drying of

out

DEPENDENCE OF PLANTS ON RADIATION

the cell walls has cut off the food supply of cells on that
side. This will result in a positive phototropic bending.
The amount of light required to induce phototropic
curvature in shoots grown in normal light is greater and
must be continued longer than that required to bring
about similar curvatures in etiolated shoots (as those
grown in the absence of light are called). Etiolated shoots
are white or pale and usually differ from normal plants in
the structure of their tissues. Also the mechanism of
bending is quite different in the two. The walls of the
cells making up the tissue in etiolated shoots contain
fat and protein, a substance similar to the white of egg.
These substances prevent the ready passage of sap and
water from the vascular supply to the meristematic tissue,
which, under favorable conditions, is capable of rapid
growth. But relatively small quantities of light produce a
photochemical action in these shoots. Protein and fatty
materials disappear from the cell walls, the fatty sub-
stances migrating mainly to the cuticle. The passageway
between the meristematic cells and their water and food
supply is thus opened up, so that in the words of Professor
Priestley, “Increased superficial growth now ensues.
Growth as a whole may be as active as ever on the more
brightly lit side of the etiolated shoot, but it is differently
distributed. More cells are added to the surface of stem
and leaf and less proportionately contributed to the inner
layers of the shoot axis. The result is, therefore, in the
aggregate, a retardation of growth in length on the illumi-
nated side and a positive phototropic curvature.”
Although many roots are not sensitive to light, there are,
as previously mentioned, a few which show negative
phototropism. The section of the root capable of bending
is situated just back of the apex or tip. In this region the
cells are rapidly enlarging by taking in water, which fills
up a space in the cell’s interior called the vacuole. Nega-
tive phototropic bending of these roots is attributed to the
increased rapidity with which these vacuolating cells

L3i2 |

pasopd aiv siaquuivys iySryT ayy Suado si ‘sapurpAd ssv[s
v ul queyd ay} Sururejuod “iaquuevyd Ja}uadg ‘Surpuaq sidosj0j0yd jo Apnys ay3 Joy xoq Jajyauojoyd yuryg

TL ALW Id

Oat seedling curved toward blue light and away from red light

PHOTOTROPISM

enlarge under the influence of light. Those on the shaded
side of the root enlarge less rapidly.

With the above explanations in mind, we may proceed
to examine the results obtained with decapitated coleop-
tiles. These organs, at the stage at which they are used in
such experiments, grow entirely by cell enlargement and
not by cell division. Light increases the rate of cell en-
largement but the final size 1s less than it would have been
without light. Each vein or water pipe running to the
tip of a coleoptile terminates in a pore. When the shoot
becomes gorged with water this pore serves as a safety
valve and frequently a drop of water is seen on the tip of
this shoot. If the water pressure is decreased in the pipe
line on one side, growth on that side is retarded. Light
makes the passage of water through the coleoptile tissue
comparatively easy, hence when one side is illuminated the
flow of water through the vein in that region is facilitated,
thereby reducing the turgor or water pressure. This in
turn retards growth on the brighter illuminated side. On
the less-lighted side growth is faster. This causes the
shoot to bend toward the light. By cutting off the tip,
water is freely lost and growth retarded. Now if half the
stub is covered so that the veins in that region are blocked,
bending due to increased rate of growth will occur even
in darkness in such a manner that the blocked veins are
on the convex side of the curved shoot.

All in all, there seems to be little doubt that the me-
chanics of phototropism is a light-growth reaction based
to a large extent on the relation of growth to available
water and food supply.

One phase of phototropism that has been investigated
in the laboratories of the Smithsonian Institution is the
effect of wave-length, or color, of light on the growth
curvatures of plants. As a first step it was necessary to
divorce the intensity effect of light from the wave-length
effect. To achieve this a long wooden light-proof box
was built containing three separate chambers or compart-

[313 |

DEPENDENCE OF PLANTS ON RADIATION

ments. In the two end compartments lights were placed,
and the central section was used as the plant chamber.
Between the plant chamber and the light chambers were
placed ray filters through which light of given colors could
be passed (Plate 71).

In one experiment with this apparatus (plant photom-
eter), red and blue lights were used. In the middle of the
central or plant compartment a very delicate instrument
was placed for determining the intensities of the lights
coming from the end compartments. When these lights
were so adjusted as to be of equal intensity a plant shoot
growing in a small glass container was placed at this cen-
tral point and permitted to grow for a few hours. When
examined it was found to have bent sharply toward the
blue light in the manner shown in Plate 72, and the de-
duction was inevitable that the blue light retarded growth
more than the red. With this type of apparatus it is
possible to evaluate the different wave-lengths in their
effect on plant growth.

The relation of radiant energy to plants is a limitless
subject, and modern science has scarcely put its foot on
the threshold of all there is to be known. Much of the
research in this field has been confined to that portion of
the great electromagnetic spectrum known as visible light.
Only those with the boldest imaginations dare dream of
what lies hidden in the regions beyond—the infra-red and
the ultra-violet.

[314]

SELECTED BIBLIOGRAPHY

CouLTer, Joun M., Barnes, Cuar.es R., AnD CowLes,
Henry C. A textbook of botany for colleges and
universities, 2 vols. Vol. 2, Physiology, by Charles
R. Barnes. New ed. rev. and enlarged by Charles A.
Shull. New York, 1930.

Ganonc, Wituiam F. The living plant; a description and
interpretation of its functions and structure.1 New
Mork sion:

Mitier, Epwin C. Plant physiology; with reference to
the green plant. New York, 1931.

Patiapin, Viapimir I. Plant physiology. Translated
by Burton E. Livingston. 3rd ed. Philadelphia,
1926.

1 A very readable account of physiological processes taking place in plants.

[315]

ve
eth

PArr VIE

MAIZE, THE PLANT-BREEDING
ACHIEVEMENT OF THE AMERICAN INDIAN
By
J. H. Kempton
Botanist, Division of Genetics and Biophysics

Bureau of Plant Industry
United States Department of Agriculture

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ear grown by the Tewa Indians; center and right, ears grown by the Navajo.

The all-rose color is rare and found only in Indian-grown corn. About half
natural size

CHAPTER I

THE, DOMESTICATION. OF PLANTS. ASA
MEASURE OF CIVILIZATION

Human progress is generally measured in terms of man’s
mechanical skill. The accepted signposts of advancing
civilization are perfected stone tools and weapons, woven
baskets and textiles, smelted metals and fired pottery, and
the wheel and arch. These undeniable attainments are
readily evaluated in our mechanistic age but they tend to
obscure man’s truly fundamental achievement—the dom1-
nation of his biological environment. Every step of the
way from utter barbarism to the present is marked by an
increase in man’s mastery of living things; and progress in
mechanics, physics, and chemistry was forced upon man
by this need to control the animate world.

In the beginning man contended with predatory animals;
later he learned to mold plants and animals to meet his food
requirements; the present day finds him struggling with
the insects and pathogenic bacteria which threaten his
existence. One after another of these biological obstacles
has been removed, and in the achievement man has left
an indelible record of his upward climb. Perhaps the
most fascinating of these records is the one that pictures
the development of agriculture. Agriculture is the very
foundation of civilization, and the primitive societies of
today owe their precarious condition to their failure, for
one reason or another, to develop an assured food supply.
Without an adequate and assured supply of food there
can be no manual arts or sciences; no leisure for abstract
thought and all that it connotes.

[319 |

MAIZE

Thousands of years ago the ancestors of civilized man
faced and solved the problem of food for all time by
profoundly altering wild plants and animals—patiently
forcing them into modified varieties. Every species of
cultivated plant and domesticated animal is a living
monument to prehistoric breeders.

Those who have not experienced the disappointments
which follow attempts to change permanently the char-
acteristics of plants and animals can have little conception
of the difficulties encountered and surmounted by early
man in shaping the life about him to meet his needs. New
chemical products or mechanical inventions can be made,
tested, and improved as rapidly as the chemist or inventor
can work, but the breeder of plants and animals is seriously
limited by the time requirements of his materials. Living
things must have time to grow and mature. Most plants
produce only one generation a year, and in many plants
and animals the period between generations is much
longer. It is clear that even slight progress from one
epoch to another, in a culture so handicapped by time,
represents a continuity of effort and a degree of skill far
greater than those required to perfect tools or weapons.
The refinement of artifacts necessitated manual dexterity
often of a high order, but improvements in technique
increased with practice, irrespective of the introduction
of new methods. Even as tools took shape under the
painstaking and laborious methods of manufacture em-
ployed by primitive man, his ideas could develop, one
process leading naturally to another. Success in the
domestication of plants was not acquired so easily. The
plant breeder needed keenness of perception to take ad-
vantage of the small variations by which plants differ
from one another, and a degree of intelligence capable of
correlating remote causes with their ultimate effects.
Mental development must have reached the stage of fore-
sight and concern for the future as well as hindsight and
interpretation of the past. Primitive peoples of the

[ 320 |

DOMESTICATION OF PLANTS

present day who have these qualities imperfectly devel-
oped occupy a correspondingly low position agriculturally
and economically.

The short span of human life was a further handicap to
agricultural advancement, since the skill of any one man
could at best extend over but twenty or thirty plant
generations.

The early agriculturists, then, did not find their crop
plants ready to hand, merely awaiting human care to
blossom forth in abundant fruitfulness. On the contrary
the first tillers of the soil could but choose the most prom-
ising sorts from among the vast welter of wild plants, all
ill adapted to man’s wants. These wild plants, no less
than the ancestors of our farm animals, had to be caught,
tamed, and slowly domesticated through the centuries.
Modern plant breeders may well be disheartened when
they stop to survey the wide gaps between our present-
day crops and the wild plants from which these were
derived.

Our admiration for the abilities of the early agricul-
turists is further enhanced when we realize that not within
historic times has a single important food plant been
added to the heritage received from the ancients. We
have remained content to increase the acreage and to at-
tempt the improvement of the plants tamed for us by pre-
historic man. This is at once a criticism of our abilities
and a tribute to the excellence of the plant culture of
early man. It might even be urged that, viewed strictly
from an agricultural angle, modern man has retrogressed
from the position of his forbears of thousands of years ago.
For although he needs new crops suitable to lands which
can not successfully compete with lands of higher pro-
ductivity in the growing of our present food crops, yet he
lacks the vision and the magic touch which enabled the
ancients to supply their wants with new domesticated
plants.

t327]

MAIZE

WHERE AGRICULTURE BEGAN

Where agriculture first began is a subject of some dif-
ference of opinion. Unquestionably there was an early
Old World center of dawning civilization in Western Asia.
Most scholars credit the peoples of this region with having
been the first to sow seeds, and estimate the probable
time of that momentous event as 10,000 years ago. So
long as the origin of agriculture is approached from the
historical standpoint the claims of regions other than
western Asia and adjoining lands stand scant chance of
being considered, and we are forced to agree that tillage
began either in Mesopotamia or Egypt. When, however,
the botanical evidence is reviewed, there is seen to be
strong reason for believing, if not in an American origin,
at least in an independent development of agriculture
by the aborigines of America.

Anthropologists are loath to concede that man existed
in America more than 20,000 years ago, a period far too
short to permit an independent initiation of cultivation
reaching the degree of excellence found by the white dis-
coverers of the Western Hemisphere. Yet they have been
gradually increasing their estimates of man’s years in the
Americas, and though the process has been slow—the esti-
mates having barely doubled in the last ten years—there
are gathering signs that its speed will be accelerated in
the next few decades. Anthropological reasoning is de-
fective in ignoring the evidence afforded by plants as to
man’s long residence in America. Nursed on a diet of
stone and metal implements, these students of early man
seem to regard the plant remains exhumed from every
burial cist as lacking substance on which to construct
theories of past habitation. Yet the differences between
American and Old World agriculture are so fundamental
that no agriculturist would consider the former to have
arisen from the latter. The counter-assumption, that the

Old World agriculture is the child of the New, is
[ 322]

DOMESTICATION OF PLANTS

much more tenable. The greater divergence between the
cultivated plants of America and their wild relatives as
compared with the domesticated Old World plants is ex-
ceptionally strong biological evidence that American
agriculture is the more ancient. This has been pointed
out by Cook. Certainly, the development of a plant like
maize from any wild form can not be conceived as the
work of any recent comer to America from Asia.

Agriculture in the Old World appears to have developed
in a nonforested region and may have been an outgrowth
of the pastoral life. Plowing was an essential part of the
technique and at an early date animals to pull the plow
were used, but the herdsman-farmer was not forced to
nurse his crop from planting to harvest. All the culti-
vated plants were grown in mass culture, whereby the indi-
viduality of the plant was lost among the thousands of
its fellows. The New World system, on the other hand,
accorded each plant individual attention. The plants
were grown in hills, each plant widely separated from its
fellows and subject, as a result, to the closer scrutiny of the
husbandman. Animals were not used and the grower was
kept in intimate contact with his plants throughout the
entire season. The American Indians were wholly plant-
minded, and this fact is accurately reflected in the plants
they domesticated.

The Old World system is typified by wheat and the
New World system by Indian corn. Each of these cereals
was confined to the hemisphere in which it had been
domesticated, until the discovery of America by Colum-
bus; after that event maize spread rapidly through
Europe and seems to have reached China early in the
16th century, while wheat gradually found a secure foot-
hold in the New World.

The people of the Old World developed a crop which
gave the greatest food value per man-hour, while the
aborigines of America achieved in Indian corn a crop
which produced the greatest food value per unit area. The

[323 ]

MAIZE

basic differences between the agricultural operations of
the two regions would be expected to produce just this
result.

While the mass system offers many advantages for a
mechanized agriculture, it must be kept in mind that both
the American and Old World systems were evolved during
the period of hand labor; for machinery entered the
agricultural field only in modern times. Undoubtedly the
American type of agriculture, in which the Indian main-
tained close association with his individual plants, was
more conducive to their improvement and to profound
alteration in their characteristics. In conformity with
this expectation, the cultivated plants of America are
found to be much more highly specialized in comparison
with their wild relatives than are those of the Old World.
Wheat, barley, oats, and rye have living wild relatives
readily recognized as the ancestors of the cultivated
forms; but the American crops, of corn, potatoes, toma-
toes, and beans, are so highly developed that the wild
plants from which they originated can not be identified
with certainty. Indeed, so far removed are the American
crop plants from their undomesticated cousins that the
direct path of their descent is shrouded in mystery.
Human deposits afford no clue to their origin, such as they
supply to the origin of the Old World cereals, and the
botanist is forced to hypothesize for American plants an
exceptionally long past beginning far earlier than 10,000
years ago, the date assigned as the beginning of tillage in
the Old World.

Tue Most ANcIENT CULTIVATED PLANT

From purely botanical reasoning, based on a detailed
comparison of maize with its wild relatives, Indian corn
may confidently be proclaimed the most ancient of the
cultivated cereals, if not of all cultivated plants. The
botanical evidence is clear and unmistakable, however
defective the historical and anthropological record may

[ 324 |

PLATE 74

Prehistoric ears of corn (natural size). Left, from grave of a Basket

Maker Indian in Utah; right, from a pre-Inca grave in Peru. Courtesy

of the Museum of the American Indian, Heye Foundation, and W. E.
Safford

Aaqysnpuy juryg Jo nevaing “Ss "A ay fo Asajinoy «*9t61 ul suvipuy
URIANIdg 3Y} Aq UMOIS YS Saavis vouy-oid v wos pawnyxa “19}Ua9 Spissoy QJary] *(2ZIS [BAN}BU) UIOD Jo Siva UBIANIIg

SL ALV Id

DOMESTICATION OF PLANTS

be. Indian corn represents the supreme achievement in
the domestication of plants.

Of all the crop plants the cereals presented the greatest
obstacle to domestication. The flowering heads, Or in
florescences, of the wild grasses are jointed in various
ways, and when mature they completely disintegrate in
the wind, thus permitting the seed to blow about and fall
upon the ground. Before plants of this sort could be
domesticated it was essential to eliminate the features
which led to the natural scattering of the seeds. To
accomplish this was no simple matter, for the very ex-
istence of the plants in the wild state meant that they had
developed an efficient means of sowing the succeeding
generations. It is not likely that the early domesticators
were actuated by the intelligent purpose their accomplish-
ments seem to demand. Unquestionably, however, they
were keenly observant and took advantage of the im-
provement (from their point of view) in their, plants that
resulted from lucky “accidents,” or mutations.

In some of the cereals, such as wheat and all the other
Old World grains, shattering, or the loss of seed from the
head when fully ripe, is still a problem for the plant
breeder. In Indian corn this difficulty has been overcome
in a manner that constitutes one of the marvels of the
plant world. The familiar ear of corn, with its regular
arrangements of seeds in even rows, is a vegetable mon-
strosity at once grotesque and supremely useful. From
the standpoint of primitive man it is difficult to imagine
how food could be grown in more perfect packages. The
seeds, securely packed on sturdy spikes, provide a de-
lectable and easily handled food long before they are
mature. This advantage, not possessed by any other
cereal, is one which many times sustained the famished
Indians when the previous year’s harvest had been
scanty. Storage, too, is simple, for the ears can be
corded in stacks and artificially dried in wet seasons—the
smoke from the drying fires of the Indians affording a

[ 325 |

MAIZE

satisfactory protection against the grain weevils. In dry
seasons the harvested crop can be placed in the sun and
moved about with facility. The husks furnish ideal string
and were often used to braid together whole bunches of
ears which then were hung out of reach of the grain-de-
vouring animals. Seed properly stored will remain viable
for a decade and seed stocks can be accumulated as an
insurance against bad years. Since corn plants depend
on the wind to effect the union of male and female gametes,
they produce a superabundance of golden-yellow pollen;
weeks before the ears are fit for food, the Indians gather
this pollen in baskets and make of it a very palatable and
nourishing soup. And this is not all, for even the para-
sites of maize are edible; the natives of Mexico regard
corn smut as a delicacy, as desirable as our edible mush-
rooms are to us.

If ever a plant could be said to be designed for the use
of man that plant is Indian corn. And in accordance with
this seemingly providential plan, maize and man are in-
separably associated in America as far back as human
remains are found. Nowhere does maize grow without
man’s aid, nor can it. Unlike the other cereals, which,
highly domesticated though they are, will sow themselves
and persist for a few generations without the intervention
of man, maize has lost all power of distributing seeds and
maintaining itself. The ear of corn accidentally covered
with soil retains the seeds intact, and if it does not rot the
seeds may germinate in a mass, but the young plants are
choked off long before they can produce the next genera-
tion. Furthermore, the Old World cereals, developed
under a system of mass planting, have not lost the ability
to grow normally in competition with weeds; but maize,
the product of individual plant culture, can not long
survive when forced to compete with weeds and other
grasses. The whole behavior of the plant bespeaks an
extensive period of human care not accorded the plants

of the Old World.
[ 326 ]

PLATE 76

Seeds of corn showing five patterns of color distribution. Twice natural
size. Courtesy of the U. S. Bureau of Plant Industry

PLATE 77

peel
NV

ol
1

® * ® b 8% = . wun

fs %
tics ad :

Savaan

&
ay

UN
; 7

ive

a.
R

‘

Ai
‘(1

Ear of Cuzco corn (natural size). This type of corn is peculiar to Peru.
After boiling the kernels are eaten one at a time as are grapes. Courtesy
of the U.S. Bureau of Plant Industry

“DOMESTICATION OF PLANTS

Clearly maize is far removed from a wild plant, and no
wild plant resembling it has ever been discovered. When
Columbus reached America he found the plant as we
know it today, and the colonists of Virginia and Massa-
chusetts were supported by varieties of maize, the coun-
terparts of which are commercial crops in the same regions
at the present time. The four hundred years of historical
record show little change in the plant; this is true also
of the many centuries preceding, the record of which is
gradually being uncovered by archeologists. Burials of
the so-called Basket Maker Indians (who were the earliest
occupants of the American Southwest of whom we have
record) in Utah yield ears of corn indistinguishable from
the varieties grown by successors of the original growers
in the same area. From the United States through
Mexico to Peru, everywhere the story is the same—maize
taken from the most ancient exhumations is fully devel-
oped. Indeed a small fossil ear has been discovered in
Peru which resembles perfectly an ear exhumed from a
pre-Inca grave, and both are beautifully matched by
ears grown in the same region by the present inhabitants
(Plate 75). Yet there can be no reasonable doubt that
human hands planted the seed from which the fossilized
ear was produced.

Thus the known record of maize in its present form em-
braces a period of many thousand years, and the plant
probably underwent a previous period of development
fully as long before it reached the perfection shown by the
fossil ear.

That the artificial development of maize had attained
a high level in very early times is attested not only
by the size of the prehistoric ears but also by their colora-
tion. It is surely no accident that maize is the most
decorative of all crop plants, and clearly the element of
art had entered into its breeding more than 2,000 years
ago. No other plant grown for food can claim the variety
of colors or the complexity of color patterns that are

[ 327 |

MAIZE

found in maize. Our modern Corn Belt varieties of the
plant are restricted to white and yellow seeds, but most
of the varieties grown by the Indians in the two Americas,
even today, are highly colored. Not only are the seeds red,
blue, black, brown, pink, purple, variegated, and spotted,
but the tassels, leaves, silks, and cobs are found in several
colors.

These colors were not preserved by chance; on the con-
trary, at least in what is now the southwestern United
States, certain families were charged with the duty of
maintaining them. At planting time, as Cushing has
shown, care was taken to insure the presence of certain
colors in each hill. There can be little doubt that the wide
range of colors is the result of man’s desire to maintain
them. Certain it is that in our corn culture, where color
other than yellow or white is not a factor, the vivid colors
characteristic of squaw corn have disappeared. The same
holds true for the corn now grown in Spain, Italy, and
Central Europe. With the exception of an occasional red
ear, all the European varieties are either white or yellow.
In conformity with their disregard of colors modern maize
growers recognize only the three general types—sweet,
pop, and field corn. The native Americans make more
subtle distinctions and prefer a certain variety for each
of many different forms of food. The Peruvians even have
a variety with such extremely large seeds that after being

boiled they are eaten singly like grapes (Plate 77).

CHAP PER IT

THE ORIGIN OF MAIZE

Matze, then, is a plant which has been cultivated for
thousands of years, meeting the food requirements of
man and beast and providing the foundations for the
three elaborate American Indian civilizations—those of
the Mayas, Incas, and Aztecs. Well may we ask where
and how this gigantic grass as we know it originated; but
its birthplace and parentage are a mystery. The wild
prototypes of most crop plants are still in existence;
maize, however, appears to be a botanical orphan and its
original home is a matter for speculation. What little is
known of the antecedents of this plant is the result of
fitting together an intricate morphological and genetic
puzzle lacking many of the major pieces.

THE PLACE OF ORIGIN

Curiously enough, the place of origin can be more
definitely determined than the manner. In fixing on the
original home of a cultivated plant, we have a choice
between two avenues of approach—one, through the
diversity of types of the cultivated plant; the other,
through its wild relatives. Vavilov, the distinguished
Russian botanist, holds that the center of domestication
of cultivated plants is the region having the greatest
diversity of types. If this hypothesis is adopted, Peru
must be accepted as the original home of maize. This
conclusion is supported by the remarkable achievements
of the pre-Incas in the domestication of plants. These
ancient peoples have to their uncontested credit the

[ 329 ]

MAIZE

potato, tomato, and peanut, to mention only three crops
now widely cultivated, and in pre-Spanish times they
regularly grew some seventy species of plants. With this
evidence of their capability in domesticating plants, it
would seem reasonable to accept the contention that
maize also was a product of their talents.

However, to conclude that the pre-Incas developed
maize would be to ignore the very important fact that
none of the existing wild relatives of maize grow in Peru.
The absence of wild relatives in any region is a very serious
objection to its choice as the center of domestication, for
obviously the ancient breeders must have had a wild plant
on which to start improvement. It is possible, of course,
that maize developed from some closely related species,
now extinct, which existed at one time in western
South America. But as there is no evidence of any such
species, current botanical opinion places the original
home of maize in North America. For it is chiefly on the
plateau of Mexico that all the close wild relatives of
maize are now found. Furthermore, Mexico has a wide
diversity of types of maize, being second only to Peru in
this respect. Finally, Peru’s superiority in diversity of
types may be explained in a manner helpful to the Mexi-
can-origin hypothesis. Geographically Peru is distin-
guished by deep narrow valleys exhibiting a climatic
range that extends from tropical to arctic; this would
naturally result in the isolation of diverse types. All in
all, therefore, it would seem more logical to select the
plateau of Mexico, probably not far from the region of
Mexico City, as the birthplace of Indian corn; most
botanists are agreed on this locality.

THe MANNER OF ORIGIN

Having chosen a place we may next consider the possible
manner of origin. Maize, known to botanists as Zea mays,
belongs to the tribe of grasses designated Tripsaceae.
This tribe is characterized by having the male and female

[ 330 ]

PLATE 78

o
—
~
~“
- -«
eres
~
ae
SRR

Color patterns in corn ears grown by (from left to right) the Osage, Hopi, Navajo,

and Uintah Ute Indians. ‘Clay -colored ears are found only among the Hopi;

solid black ears are rare in North America, though common in Peru and Bolivia
About half nacaral size

THE ORIGIN OF MAIZE

flowers borne on separate flowering heads, or inflorescences,
or on separate parts of the same inflorescence. This sep-
aration of the sexes is a fundamental botanical distinction
and indicates that the genera which comprise the Trip-
saceae are closely related. There are three genera of
American plants which belong to the Tripsaceae: Trip-
sacum—from which the tribe takes its name—Euchlaena,
and Zea, the two former occurring as wild plants in North
America and the latter being our cultivated Indian corn.
There are numerous species of Tripsacum, two or possibly
three species of Euchlaena, and only one species of Zea—
namely, mays.

In the species of Tripsacum the male and female flowers
are in the same panicle or inflorescence, the female flowers
being borne on the lower and the male flowers on the upper
sections of the branches (Fig. 53). In Zea mays, or Indian
corn, the two sexes are in separate inflorescences. The
male flowers are confined to the terminal inflorescence, or
tassel (except in certain abnormal forms), and the female
flowers are borne on the ear, half way down the plant.
The plants of Euchlaena fall midway between those of
Tripsacum and Zea with respect to the separation of the
sexes. In Euchlaena the terminal panicles of the main
plant and of the primary lateral branches bear only male
flowers, as in Zea; but the female flowers, which are borne
on secondary lateral branches, often terminate in a male
spike, thus closely approximating the arrangement found
in Tripsacum.

In general appearance Euchlaena more closely resem-
bles Zea than Tripsacum, and since both Zea and Eu-
chlaena are more highly specialized than Tripsacum, the
latter is considered to be farther back in the evolutionary
scale.

All the botanical evidence shows that the closest wild
relatives of maize are the two species of Euch/aena, one an
annual, the other a perennial. Both species are now known
under the Aztec name of feosinte, translatable as god grass

[331]

MAIZE

~~
Ny

4
.
2

i
|
i

/ { Q / | =
- = t 7 L ts As: ~
— rt Ai f- f
P= = } : SS
= = A\S Waes LY = A =| —
: A t TA ES +s FN Saget ——
os 0 i Ck LA NY ox n3 | ¥ =
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Fic. 53.

he base of the tassel,

Inflorescence and section of a leaf of Tripsacum pilo-

sum. The female flowers are borne at t

which resembles that of corn

PLATE 79

Two relatives of maize

Tripsacum pilosum, growing natu- -Euchlaena mexicana, growing un-
rally on the west coast of Mexico — dercultivation in the United States

Courtesy of the U. S. Bureau of Plant Industry

A normal corn plant.

PLATE 80

Courtesy of the U.S. Bureau of Plant Industry

THE ORIGIN OF MAIZE

or god grain. The annual form has gained, within the last
fifty years, some importance as a forage crop in the south-
ern United States. Like their cultivated cousin, maize,
these two wild relatives provide some baffling problems
for the botanist. The annual species (Euchlaena mexicana)
became known through an introduction of seed to Paris.
This seed was supposed to have come from Santa Rosa,
Guatemala, yet diligent inquiry and several explorations
have failed to discover either species of Euchlaena growing
wild in Guatemala. The evidence for the occurrence of
Euchlaena anywhere outside of Mexico is purely literary
and is confused by attaching to this species the name
teosinte, which is everywhere used by the natives of Mexico
and Guatemala for various species of Tripsacum. The
confusion of names and the entrance of Euchlaena into
commerce need not concern us in our inquiry as to the
origin of maize, but they serve to illustrate the involved
evidence with which we must deal.

The perennial species of Euchlaena (E. perennis)
known only from a very restricted region west of Guada-
lajara, Mexico, in the vicinity of Ciudad Guzman, while
the annual species (EZ. mexicana) extends from south-
western Chihuahua to the region about Mexico City.
Euchlaena has been reported also from western Oaxaca
and possibly Chiapas, but no authentic specimens from
wild plants have been collected from either of these
regions.

Both species of Euchlaena occur as weeds on the margins
of cultivated maize fields, and indeed can hardly be ex-
pected anywhere else, as corn is now grown in practically
every location that would provide a suitable habitat for
these plants. Thus even the wild relatives of maize are
forced into intimate association with man. Most of the
present growers of Indian corn in Mexico are unaware of
the close affinity of Euchlaena and maize, though a few
recognize that Euchlaena hybridizes with corn and is
therefore detrimental.

| 333 |

MAIZE

Neither species of Exch/aena is at all adapted for human
food and there is no historical or archaeological evidence
that either was ever so used. The seeds are embedded

Fic. 54. Left, inflorescence of Tripsacum dactyloides, with
female spikelets below paired male spikelets; right, separate
male and female inflorescences of Euchlaena mexicana; the spikes
at the left of the tassel of E. mexicana have been dissected

a9 ”

from an “ear” similar to that on the right

in a hardened segmented rachis, or stem, closed by a
shell-like outer glume, or bract (Fig. 54). The segments
are arranged end to end, each containing a single seed,

[ 334 ]

THE ORIGIN OF MAIZE

and an inflorescence consists of from six to ten segments.
When ripe the rachis is very brittle and the segments
break apart scattering the seed on the ground. Although
the segments of the rachis are about the size of a seed ‘of
pop corn, the actual seed of Huchlaena, inclosed in the
segment, is much smaller than a grain of wheat. From
the standpoint of primitive man, EKuch/aena offers a very
poor source of food. To separate the seeds from their
outer covering is a laborious process and to gather seeds
in any quantity requires an almost daily harvest during
the ripening period of at least two months.

Both species of Euchlaena hybridize with maize.
(Among plants no less than among animals related species
sometimes cross.) When the hybrids are fertile the rela-
tionship of the parents is thought to be close, whereas
sterile hybrids furnish strong presumptive evidence of a
more remote relationship. Hybrids between genera are
extremely rare and only a few examples are known among
plants, one being the Euch/aena-maize cross.

The annual species (E. mexicana) crosses freely with
corn, and the various hybrid generations are perfectly
fertile (Plate 81). Indeed, in all the regions in Mexico
where E. mexicana is found: maize-Euchlaena hybrids are
common. So general is the hybridization between these
two species that it is doubtful whether a pure form of
E. mexicana, uncontaminated with corn, exists in Mexico.
In the lake region, south of Mexico City, the various
grades of hybrids occupy whole fields and are prominent
plants in the landscape. Such natural mongrelizing 1s
excellent evidence of the very close relationship between
Zea and Euchlaena but affords no basis for the assumption
that Indian corn was derived from Euch/aena by selection.

Hybrids between the perennial species (E. perennis) and
maize are much less common. In the fields of E. perennis
and maize, west of Guadalajara, we found but a single
hybrid plant, a very decided contrast to the fields of
E. mexicana and maize elsewhere in Mexico. Controlled

[335]

MAIZE

hybrids between E. perennis and maize have been made
in this country with plants of Ewch/aena imported for the
purpose. The cross is made with difficulty and the hybrid
plants, except under unusually favorable conditions, are
sterile. This sterility, fundamental in nature, is explained
by the wide cytological differences between Zea and E.
perennis.

The whole question of the derivation of maize from
either or both of the two species of Euchlaena is highly in-
volved and is one on which botanists are not agreed.
Early investigators accepted the numerous natural hybrids
between maize and E. mexicana as representing transitions
from Euchlaena to maize, and even in more recent times
Burbank fell into the same error. This assumption that
the steps in the evolution of maize are being continuously
repeated before our eyes is now recognized as wholly in-
correct and in fact modern genetic experiments suggest
that the whole picture should be reversed. There are
many indications that E. mexicana has been derived from
hybrids between E. perennis and maize—an hypothesis
which if substantiated will remove E. mexicana from all
consideration as one of the probable ancestors of maize.

Although there is a fundamental botanical relationship
between Euchlaena and maize it is difficult to see how the
latter could be developed from the former by means of
selection. The salient characteristics of Indian corn,
which make it so useful to man, are not found even in
rudimentary form in Euch/aena.

The ear of corn remains a botanical conundrum with no
counterpart in any other grass. There is no difficulty in
tracing the successive stages in the alteration of the wild
relatives of most cultivated plants which made them
suitable for cultivation. There is no element of uncer-
tainty as to how the head of wheat developed, for in its
essential features it is the inflorescence of wild wheat; and
as with wheat so with the other Old World cereals—no
profound morphological changes from their wild proto-

[ 336 ]

PLATE 81

Pistillate inflorescences of Euchlaena mexicana (upper left) and of

Euchlaena-maize hybrids as they are found on the margins of Mexican

corn fields. Slightly reduced. Courtesy of the U.S. Bureau of Plant
Industry

PLATE 82

Evidence for fusion as origin of corn ear

Section of an eight-row ear Tassel of corn showing bifurcated

of corn showing separation at central spike suggesting origin by fusion

Courtesy of the U.S. Bureau of Plant Industry

THE ORIGIN OF MAIZE

types have taken place. Maize, on the other hand,
presents a baffling mystery, for the ear of corn is not fore-
shadowed by any simpler organ in its relatives. Nothing
resembling the ear of maize is found in any other of the
grasses, nor are there any rudimentary organs in this great
family of plants that can be conceived to contain the germ
of an ear. It is known, of course, that the ear developed
from a branched structure similar in form to the tassels
of maize and Euchlaena. But how such a branched in-
florescence was changed to bring about the many-rowed
ear is still a matter of speculation.

Not the least of the difficulties encountered in attempt-
ing to derive a single spike from a complex inflorescence
is the contradictory evidence afforded by the ear itself.
At first thought it would seem a simple matter to reduce
a ramified panicle to a spike by suppressing the branches,
and this hypothesis early was advanced to explain the ear.
Support for this view was derived from the obvious homol-
ogy of the ear with the central spike of the tassel and
by the various stages between ears and tassels found on
the terminal inflorescences of tillers or lateral branches.
The objection to this explanation lies in the fact that the
central spike of the maize tassel is as much in need of an
explanation as the ear. None of the relatives of maize
has tassels terminating in many-rowed central spikes.
The uppermost branch, or spike, in the tassel of Euchlaena
and of Tripsacum is exactly like all the other branches in
having only four rows of spikelets on a flattened axis,
whereas the terminal spike of a maize tassel is a cylindrical
affair with eight or more rows of spikelets arranged in
groups of two around the entire axis (Fig. 55).

Granting that the ear of corn is the homologue of the
central spike of the tassel, differing from it chiefly in
having only female flowers and membranaceous glumes,
the problem of the formation of the ear is not solved but
becomes one of explaining the central spike. Three
theories have been advanced as to how this organ could

[ 337 |

Fic. 55. Left, central spike
of a maize tassel, compared
with (right) the tassel, or
male inflorescence, of

HH i Euchlaena mexicana
Atl ”
Wy | | | \\
S i} S

THE ORIGIN OF MAIZE

be derived. These may be designated briefly as fasciation,
branch suppression, and twisting. All three are in good
standing at the present time and have reputable adherents.

The theory that the central spike, and hence the ear,
arose as the result of the fasciation, or growing together,
of two four-rowed branches is beautifully supported by
many examples of obviously fasciated ears and central
spikes. Eight-rowed ears of corn which are divided for
half their length into two four-rowed segments are found
frequently and a similar condition is often met with in
central spikes (Plate 82). Furthermore, true-breeding
races with fasciated ears, and central spikes as well, have
been isolated by geneticists, showing that fasciation is not
only possible but is hereditary in maize.

The hypothesis of branch suppression is equally well
supported by a true-breeding type of maize known to
geneticists as ramose. In this type both the ear and tassel
are very much branched inflorescences which in extreme
cases lack central spikes (Plate 83). The various degrees
in the expression of this branched-ear character show
clearly that branches often are reduced to paired spikelets
and when such a reduction occurs a central spike is
formed. The ramose type of maize arose as a mutation
from the normal form and behaves as a simple Mendelian
recessive in inheritance. In crosses with Euchlaena the
character reappears in the second generation in approxi-
mately the expected proportions but greatly modified in
expression.

The third method proposed for deriving the ear, that
is, by twisting the axis of a simple inflorescence, is sug-
gested and supported by Euchlaena-maize hybrids. In
the second generation of these hybrids all stages are
found from the simple two-rowed spike of Euchlaena with
segmented rachis to the multiple-rowed unsegmented
rachis of the maize ear (Plate 84). These stages afford
clear-cut examples of how an ear can be built up by
twisting a two-rowed axis and solidifying the rachis. The

[339 |

MAIZE

first stage of twisting results in a four-rowed ear, which
passes by imperceptible stages to ears with higher multi-
ples of rows. It is apparent from these hybrids that there
is no insurmountable obstacle to combining the widely
different characteristics of the pistillate inflorescences of
Euchlaena and maize; and the inference is that a com-
parable combination may have taken place in the develop-
ment of maize.

In the present stage of our knowledge these three
hypotheses as to how ears were formed stand on an equal
footing of credibility and no decision can be rendered as
to which is the one most likely to have occurred.

Even with a moderately satisfactory picture of how an
ear of corn could be built up from a branched inflorescence
similar to a tassel of Euchlaena, we have gained little or no
knowledge of how the process came about.

Since Euchlaena hybridizes with Zea and closely re-
sembles it in many respects, there can be little doubt that
the relationship between these two genera is very close.
Euchlaena, being a wild plant fully capable of self-propa-
gation, would seem at first glance to be the logical ancestor
of maize; but whether the relationship is one of parent and
offspring is not so certain. The detailed botanical and
morphological evidence affords serious objections to such
an hypothesis.

The flowering unit of the grasses is the spikelet, which
in normal maize and Euchlaena bears flowers of only one
sex. The staminate, or male, spikelets contain two flowers,
each with three stamens; but the pistillate, or female,
spikelets normally have only a single flower. In Euchlaena
the spikelets rarely develop flowers of both sexes, but
maize frequently produces bisexual spikelets both in the
staminate and pistillate inflorescences. This evidence in-
dicates that the separation of the sexes occurred later and
is less complete in Zea than in Euchlaena. Such a conclu-
sion is further supported by the greatly modified rachis, or
flowering stem, and outer glumes of the female inflo-

[ 340 ]

THE ORIGIN OF MAIZE

rescence of Euchlaena. In maize the bracts, or glumes,
surrounding each seed are not greatly differentiated from
those inclosing the staminate flowers of the tassel, whereas
in Euchlaena the outer glume of the pistillate spikelet has
become thickened and hardened. Furthermore, in maize
the spikelets are borne in pairs—one, pediceled, or stalked,
the other, sessile—and this pairing is normal for both ale
and agli inflorescences. In Euchlaena the staminate
spikelets are paired as in maize but the pistillate spikelets
are borne singly—the pediceled spikelet being aborted.

These differences between maize and Euch/aena in the
separation of the sexes and development of the flowering
parts show that maize is less highly specialized in an
evolutionary sense than is Euchlaena.

The customary explanation that maize evolved from
Euchlaena by gradual changes aided by human selection
ignores the point that neither species of Euchlaena, as
growing at present, could be considered as furnishing a
basis from which to start selection toward maize. The
male and female inflorescences of Euchlaena are already
more highly differentiated in many respects than the
staminate and pistillate inflorescences of maize. There-
fore, to derive maize from Euchlaena by selection would be
to pass from the specialized to the unspecialized—a
reversal of the usual direction of evolution. Furthermore,
if it is assumed that the change was gradual, it is hard to
believe that some of the intermediate stages would not
have been preserved, at least in the ancient tombs of man,
if not as living plants.

Hysrip OricIN oR DEVELOPMENT BY SELECTION

There is still another hypothesis for the origin of maize.
Collins having noted the many resemblances between
maize and the Andropogoneae, a very large family of
grasses, which includes the broom sedge, suggested that
the former may have arisen as the result of natural hy-
bridization between Euchlaena and some grass similar to a

gan |

MAIZE

species of the subgenus Sorghum of the genus Andropogon.
This genus in the Old World has furnished a series of
domesticated forms grown for grain, syrup, and broom
material. In many respects it is similar to Zea, the genus
to which maize belongs, the two genera being parallel
cytologically and having several inherited characteristics
in common. Some of the true-breeding abnormal forms
of maize so closely resemble those of the cultivated
Andropogoneae as to be botanically indistinguishable
from them.

Numerous attempts have been made to cross maize and
members of the Andropogoneae, but without success. It
is true that Burbank claimed to have made the cross,
but investigation showed this to be an error arising from
some close resemblances between a variety of pop corn
and one of the grain sorghums.

None of the Andropogoneae which would logically be
chosen as the mate for Euchlaena to produce a hybrid
from which maize might descend are indigenous to the
New World. However, in view of the intermediate posi-
tion of maize between Euch/aena and the andropogons, the
idea of the cross having been made with a New World
species may be entertained. Not only does this hypothesis
harmonize with the known morphological facts but it
reduces very materially the length of time necessary to
produce such a plant as maize.

When the hypothesis of hybrid origin was first put forth
the idea was considered as a novel one to be invoked only
as a last resort. Since that time, however, claims have
been made for a hybrid origin of wheat, barley, apples,
and grapes among our crop plants, and cattle, swine,
sheep, and chickens among our domestic animals.

The alternative to hybrid origin is development by
selection. No two plants are just alike, for all organisms
are subject to variation. When the variations are herit-
able in nature it is possible to change, within limits, the
type of organism by selecting for propagation only those

[ 342]

PLATE 83

Longitudinal section through an ear of ramose corn, showing how the
normally sessile spikelets have developed into branches. Natural size.
Courtesy of the U. S. Bureau of Plant Industry

PLATE 84

Inflorescences from Euchlaena and Euchlaena-maize hybrids, showing the
stages between a Euch/aena spike and an ear of corn (natural size). Spike

at upper left is the commercial type of E. mexicana, and adjacent spike is
the native Mexican form. Courtesy of the U. S. Bureau of Plant Industry

THE ORIGIN OF MAIZE

individuals which have the desired characteristics. This
process has been employed in the development of most
of our improved varieties of crop plants and animals.
Modern breeding experiments show that the procedure
does not stimulate the organisms to vary further in the
direction of selection, but that the breeder is limited to a
choice of individuals which happen to change toward the
desired ideal. Thus the breeder of race horses uses for
parents the fastest animals; the dairyman, the highest
milk producers; the poultryman, the best layers. Simi-
larly with plants—those with the highest yield, finest
quality, or greatest resistance to disease are chosen,
whenever they appear, as parents for the succeeding
generations.

Many botanists of the formal school prefer the hypothe-
sis that the crop plants were developed from their wild
ancestors by this very gradual process of selection, and
they still view hybridization as a rare event not to be
seriously considered as a factor in the development of our
present-day crops. Maize and Euch/aena are held to have
developed by gradual evolution from a common ancestor
probably closely resembling Tripsacum, of which several
species are indigenous to North America. The presump-
tion is that the direction of evolution of maize was con-
trolled, at least in the later stages, by human selection.
Such a process would require a lapse of time far beyond
that available on even the most liberal estimates for the
beginnings of agriculture.

If selection is deemed to be too slow, the phenomenon
of mutation, or sudden large changes in type, 1s suggested.
By hypothesizing mutation in the gross sense it is possible
to form any sort of plant almost over night, as it were,
and one need not be restricted as to ancestry. Thus it
could be claimed that the present-day maize plant arose
as an abrupt change or mutation either from Euch/aena or
almost any other grass. Such large-scale mutations are
unknown in any organisms and are hardly to be expected.

[ 343]

MAIZE

It is possible, of course, to conceive of several rather large
mutations which together resulted in maize, but if they
occurred from existing wild plants it would be expected
that they would recur from time to time.

Mutations in maize as in most other organisms in-
tensively studied are, of course, far from rare. Within the
past few years several hundred such changes have been
noted affecting many parts of the plant. The color of the
seeds may mutate from red to variegated or the reverse,
green plants may give rise to white ones, normal seeds to
defectives, tall plants to dwarfs, and so on through the
whole range of plant parts. For the most part these
changes or mutations are undesirable in that they result
in weak plants that are not as productive as the normal
form, and their elimination from seed stocks is the aim of
modern maize breeders. The observed mutations affect
single characters or small groups of characters and are of
a different degree of magnitude from those necessary to
account for the origin of a plant like maize from its wild
relatives. They represent changes in single hereditary
units and behave as simple Mendelian characters. When
crossed with the forms from which they arose they always
reappear unaltered in subsequent generations. Crosses
between maize and Euchlaena exhibit a complete blending
of the characteristics of both species. There is no alterna-
tive segregation into the parental forms, and the evidence
clearly shows that these species differ from one another
not by a single hereditary unit but by literally hundreds
of genes. If we are to derive maize from Euchlaena by
mutation we must accept the evidence and conclude that
not one but hundreds of mutations have occurred, and
that is in effect a return to the hypothesis of selection.
That maize differs so widely genetically from Euch/aena,
its closest relative, does not preclude their both having
arisen by mutation from some distant ancestor; but if the
relationship between these two species is as remote as this,
it is difficult to explain their fertility when crossed.

[344]

PLATE 85

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Examples of a color mutation in corn. The large colorless areas result
from an abrupt change in the gene that controls the development of
variegated pericarp. Courtesy of the U.S. Bureau of Plant Industry

THE ORIGIN OF MAIZE

Curiously enough, in comparison with maize its wild
relatives are remarkably stable—a stability that affords
additional evidence that maize is in fact a hybrid. Thus
normal maize plants range in height from six inches to
twenty feet; the leaves vary in length from six inches to
four feet, and in width from a half inch to six inches; the
ears range in length from one inch to twenty inches; the
number of seeds vary from less than one hundred to over
a thousand; the weight of the seeds may vary from one-
tenth of a gram to more than a gram, and they may
range in length from three millimeters to two centimeters.
These are only a few examples of the variability of this
species, for practically every organ is found under a wide
range of sizes, shapes, and colors. Nothing approaching
this degree of variability is found in any of the maize
relatives. Indeed the entire range of characters in all the
other New World members of the Tripsaceae tribe com-
bined does not equal that of Zea alone.

The chief objection to the mutation hypothesis—aside
from the facts that large mutations are extremely rare
and that the relatives of maize are stable—is the remark-
able parallelism between the types of maize wherever
found. All forms and sizes of maize are perfectly fertile
in crosses. Only an expert can distinguish many of the
Peruvian varieties from those of our southwestern Indians,
a fact which indicates clearly that the distribution of this
important food plant did not take place until it was a
finished product morphologically speaking. Further evi-
dence for this point is found in the wide distribution of
colors, seed types, and plant forms. Some differences
exist, It is true, but these are insignificant in comparison
with the large number of similar types grown in widely
separated and remote regions.

On the mutation hypothesis one would expect that the
first change in form that resulted in a plant of economic
usefulness would have started the chain of distribution
so that the farther ends of this hemisphere would have had

[ 345 |

MAIZE

a cereal crop descended from pre-maize plants of this sort.
The subsequent mutations would have occurred in widely
separated regions, and it is extremely doubtful whether
trade conditions among the aborigines would ever have
brought all the stages together. Unless the intermediate
forms were assembled and intercrossed, various degrees
of maizelike plants should be found throughout the New
World. But nothing like this occurs, and maize, exactly
as we know it today, appears to have been distributed
from Peru to New Mexico thousands of years ago.

THE CROWNING ACHIEVEMENT OF THE AMERICAN INDIAN

Whether selection, hybridization, mutation, or a com-
bination of all three is eventually settled upon as the
answer to the origin of maize, botanists are agreed that
the American Indian played the largest part in the de-
velopment of this remarkable grass. To him and to him
alone belongs the credit for bringing this cereal to its
present high stage of development. He it was who dis-
tributed it throughout the New World and, with a pa-
tience only equaled by the Chinese, slowly pushed the
frontiers of maize culture across the deserts to the fertile
plains of the north, and through the tropical jungles to
the temperate south. To his efforts the world owes the
only cereal which can be cultivated from Canada to
Chile, producing food almost equally well in the short
seasons of the far north and extreme south and in the
twelve-month season of the Tropics.

Thus, for unknown centuries maize has been intimately
associated with the life of man in the Western Hemisphere.
From the plains of southern Canada, across the table-
lands of Mexico, through the deep valleys of the Andes,
to southern Argentine this splendid grass has provided
not only the chief food of the inhabitants but their
artistic and literary inspiration as well. And how per-
fectly they saw the details of this, the crowning achieve-
ment of their plant genius. The conventionalized maize

[ 346 |

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THE ORIGIN OF MAIZE

plants drawn as decorative motifs on the pottery of Peru
(Fig. 56) at once attest the artistic ability of the ancient
Peruvians and show a familiarity with their subject far
superior to that of the early Caucasian illustrators. Ears

Fic. 56. Conventionalized corn plants drawn on a clay vessel
by the people who preceded the Incas in Peru. After Lehmann

of corn, skillfully molded, adorn ceramics from Mexico
and Peru, furnishing imperishable records of the high
level of the ancient maize culture.

Following the return of Columbus, maize spread rapidly
across southern Europe, through Burma, and seems to
have reached China in the 16th century. At the present
time it is found in the most remote and inaccessible regions
of Asia and the islands adjoining that continent. Although
this majestic emigrant did not supplant the Old World
cereals—wheat, rice, and barley—as a basic food, it
found a dignified place in the agriculture of the great
plains of central Europe. In the picturesque province
of Burma it contributed to the popularity of that other
great American traveler—tobacco—by furnishing the
wrappers for the “whacking white cheroots.”’

The Orientals, like the American Indians, early appre-
ciated the artistic possibilities of maize, as is shown by a

[ 347 |

MAIZE

beautifully executed 16th century screen now in the
Freer Gallery of Art, at Washington. No more pleasing
reproduction of the maize plant can be found than in this
four-hundred-year-old garden scene (including, by the
way, the Peruvian-bred Amaranthus), for not only have
the plants been balanced skillfully but they have been
reproduced with a fidelity to nature superior to contem-
poraneous European attempts.

Though banished from the arts when our industrial
civilization submerged our agricultural antecedents, maize
has found a place in the halls of science by providing a
valuable tool for the study of heredity. It is on this
score that we are now concerned with the origin of this
plant. The American Indians no less than we moderns
were sorely perplexed over the genesis of their majestic
plant, but where we debate the merits of this or that
botanical hypothesis they had recourse to chanted sagas
recounting godly gifts and the intervention of the im-
mortals. And who can say where lies the truth? For
as the Zuni have said “Men, our children, are poorer than
the beasts, their enemies; for each creature has a special
gift of strength and sagacity, while to men has been
given only the power of guessing.”

[ 348 |

SELECTED BIBLIOGRAPHY

Coxtiins, G. N. Notes on the agricultural history of
maize. Ann. Rept. Amer. Hist. Assoc. for Ig1g,
Vol. 1. Washington, 1923.

—— The phylogeny of maize. Torrey Botanical Club
Bull., Vol. 57. New York, 1930.

Cook, Orator F. Peru as a center of domestication.
Jour. Heredity, Vol. 16, Nos. 2 and 3. Washington,
1926.

— "The American origin of agriculture. Pop. Sci.
Monthly, Vol. 61. New York, 1902.

CusHinc, Frank Hamittron. Zufhi breadstuff. Indian
notes and monographs, Mus. Amer. Indian, Heye
Foundation, Vol. 8. New York, 1920.

Kempton, J. H. The ancestry of maize. Washington

Acad. Sci. Jour., Vol. 9, January, 1919.

Maize and man. Jour. Heredity, Vol. 17, 1926.

WEATHERWAX, PauL. The story of the maize plant.
Chicago Univ. Science Series. Chicago, 1923.

Part VIII

BOTANICAL EXPLORATION IN SOUTH
AMERICA
By
ExuiswortuH P. KI.uip

Associate Curator, Division of Plants
United States National Museum

PLATE 87

Vegetation of the subtropical zone in Colombia. The epiphytic growth
includes filmy ferns, bromeliads, aroids, and orchids. Ropelike lanas
swing from the trees. By E. Cheverlange

CHAPTER I
A NEW FIELD FOR AMERICAN BOTANISTS

Tue territorial expansion of the United States, with a
corresponding development of means of transportation,
gave the American botanist of the last century wonderful
opportunities for exploration. Confined at the beginning
of the century to the Atlantic seaboard, he saw the West
rapidly open up to him, and by the time the hundred
years had run out, he had collected substantially all the
kinds of plants growing within the continental United
States. True, certain areas required further intensive
study, and a vast amount of information had to be as-
sorted and put into intelligible form; but the eyes of the
ever-curious explorer were turned toward our island pos-
sessions and to the little-known parts of the New World.

It was to Mexico that the American botanical collec-
tors first went. The appeal of that vast republic, lying
so extensively within the Tropics and having an altitudinal
range of thousands of feet, was especially great. Pringle,
Rose, Palmer, and Nelson traversed Mexico from the
northern boundary to Yucatan and from the Atlantic
to the Pacific, and upon their collections is based a large
part of our present knowledge of the flora of Mexico.
American botanists have found their way, also, to allthe
countries of Central America and to the Bahamas, Cuba,
Porto Rico, Haiti, the Dominican Republic, Jamaica, and
the Lesser Antilles, and descriptive accounts of the vegeta-
tion of several of these regions have been published.

But until very recent years the great South American
continent has remained almost wholly unknown to the

[353 |

EXPLORATION IN SOUTH AMERICA

botanical explorers of the United States. And when
about thirteen years ago certain American scientific in-
stitutions seriously commenced the exploration of South
America, they found that much work had already been
done by European explorers. Thousands of specimens
had been collected and deposited in European herbaria.
South American botanists had explored their countries
extensively, but they, too, had sent their collections to
Europe, not to the United States.

The earliest pressed plants to reach Europe from South
America were doubtless those sent by missionaries or
casual travelers. Some attribute of the plant, perhaps
some medicinal property, aroused the visitor’s interest,
and he sought to make vivid his description to those at
home by sending a sample of the plant. Some of these
specimens eventually reached botanical students, who
wrote about them. Then the botanists themselves went
to South America, often attached to general exploration
parties. Horticulture gave a decided impetus to botanical
exploration. The sovereign or the large landowner would
desire to grow the gorgeous tropical plants in his gardens,
and would commission a collector to go to South America
and gather seeds, bulbs, and young plants. For many
years the large horticultural houses of Europe main-
tained explorers in various parts of South America.

It is not possible here to give even a brief summary of
the work done by all these men. The accounts of their
travels and adventures, their comments on the life of
the people they met with, their observations on the plants
and animals make fascinating reading. In these men
one sees little resemblance to the conventional portrayal
of the botanist as a shriveled old man, wandering about
abstractedly, peering intently through a little lens at some
dainty flower.

Except for the expedition under the leadership of
Commander Wilkes, sent around the world by the United
States Navy in 1838 to perform a general scientific survey,

[354]

A NEW FIELD FOR BOTANISTS

we find no record of important exploration in South
America by North Americans until the latter years of the
century. Then came Rusby’s expeditions to Bolivia and
Morong’s to the more southerly countries. Finally in
1918 a plan was formulated by the New York Botanical
Garden, the Gray Herbarium of Harvard University, and
the Smithsonian Institution for the cooperative explora-
tion of the northern part of South America. The plan
contemplated the sending of expeditions into the field
whenever practicable; regions already explored by earlier
collectors were to be revisited and efforts made to re-
collect the species little known to American botanists;
regions wholly unknown botanically were to be explored
for the first time; finally, when a sufficiently large amount
of material had been collected descriptive accounts of the
vegetation of these northern countries were to be pre-
pared.

In the carrying out of the project other institutions have
given assistance at various times, and as a result two ex-
peditions have gone to British Guiana, one to Venezuela,
two to Ecuador, and three to Colombia. Although these
parties penetrated far inland from the coast, of such ab-
sorbing interest was the collecting that time permitted
only a view of the vast Amazonian basin from the moun-
tain heights. So, except for the recent work about Mount
Roraima and Mount Duida of G. H. H. Tate, of the
American Museum of Natural History, the southern por-
tions of British Guiana and Venezuela, southeastern
Colombia, and eastern Ecuador still remain unexplored.
Although not directly connected with the cooperative
program for exploration in northern South America, an
expedition was recently (1929) sent by the Smithsonian
Institution into northeastern, or Amazonian, Peru, and
the collections obtained on this trip give an idea of the
general nature of the vegetation of the Amazonian forests
on the north.

The three expeditions to Colombia and the recent one

[355]

EXPLORATION IN SOUTH AMERICA

to eastern Peru serve well to illustrate the whole subject
of the botanical survey of South America. For Colombia
—with a frontage on both oceans and with three great
mountain ranges, peaks of which exceed 18,000 feet in
height—offers nearly every type of coastal or mountain
collecting that is to be encountered anywhere in South
America; and eastern Peru is representative of the vast
forested area occupying the central part of the continent.
The problems which confront the explorer of Colombia
and of eastern Peru are essentially the same as those which
must be met by the explorer of the ocean strip of Vene-
zuela, of the mountains of Ecuador and Chile, or of the
rivers of British Guiana and Brazil.

TorpoGRAPHY AND VEGETATION OF COLOMBIA

Colombia is the fourth largest of the South American
republics and the only one with long coast lines on both
the Atlantic and Pacific oceans. If superimposed on a
map of the United States it would reach approximately
from Lake Ontario to central Georgia and from the
Atlantic Ocean to Illinois. In latitude it extends from a
little beyond 12 degrees north of the equator to about 2
degrees south of the equator. In altitude it ranges from
sea level to some 18,500 feet above sea level. At the
border between Ecuador and Colombia the Andes moun-
tain chain divides into three branches, known as the
Western, Central, and Eastern cordilleras. Between the
Western and the Central cordilleras lies the Cauca Valley;
between the Central cordillera and the Eastern cor-
dillera the Magdalena Valley. To the southeast is a
vast region, constituting nearly half the area of the re-
public, of low elevation, forming a part of the Amazon
and Orinoco drainage basins. Then there are the Atlantic
and Pacific coastal strips, respectively, at the extreme
north and west.

Except at their southern extremity the three great
mountain ranges are distinct from each other, though near

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PLATE 89

A lupine from the Paramo del Quindio, Colombia. Note the dense
woolly covering of the plant. Photograph by T. E. Hazen

A NEW FIELD FOR BOTANISTS

Medellin, in the Department of Antioquia, the distance
between the Western and Central ranges is only the width
of the Cauca River itself. Elsewhere the Cauca Valley is
twenty to thirty miles wide, and the Magdalena Valley
at most points even wider. Both the Western and the
Central cordilleras terminate in northern Colombia; the
Eastern range divides near the city of Bucaramanga, one
branch extending northward a few hundred miles, the
other passing on into Venezuela. Isolated from these
great cordilleras, the Santa Marta mountains occupy a
small area in northern Colombia, rising directly from the
sea to a height of more than 18,000 feet.

This remarkable topography at once gives rise to sev-
eral questions as to the distribution of plants. Are the
plants on each of the cordilleras essentially the same or
strikingly different? Do Ecuadorean species extend north-
ward, and if so, do they follow all the ranges? Is there
any similarity between the plants of the Western cor-
dillera and those of the mountains of Central America?
If so, this might indicate that a connecting link between
the two once existed. Do the plants of the Cauca Valley
“jump” over the mountains to the Magdalena Valley?
How does the flora of the Pacific slope compare with that
of the Atlantic coastal area? Is the vegetation of the
Amazon basin of southeastern Colombia like that of
the Magdalena Valley and other low-lying parts of the
country? Other questions concern the influence of altitude.
How do the plants at the base of a mountain range com-
pare with those at 8,000 feet and those at 15,000 feet?
Are there well-marked zones of vegetation dependent on
altitude? Are the plants of the cool-temperate altitudes
closely related to the plants of the north temperate zone
of the latitude of New York, for example, or are they
modifications of the tropical plants occurring within a few
miles of them, though lower by several thousand feet?

To assemble data for answering these questions, plans
for the exploration of Colombia were made, which called

[357]

EXPLORATION IN SOUTH AMERICA

for work in each of the cordilleras at southern, central, and
northern points and at various altitudes; in the Cauca
and Magdalena valleys; in the Amazon and Orinoco
basins; and on the Pacific slope and the Atlantic seaboard.
A part ‘of this work has been accomplished; much remains
to be done. Some general observations may be made
upon the distribution of plant life in Colombia, but
definite answers to many of the questions must await
careful study of the vast amount of herbarium material
collected.

In going from sea level to the snow line in Colombia
the traveler passes through various zones of vegetation,
much as he would if traveling from the Equator to the
North Pole near sea level. The boundary line between
the zones is not always a sharp one, nor is it always at the
same altitude. But with little difficulty one may recognize
four distinct belts.?

The tropical zone lies between sea level and an altitude
varying from 4,500 to 6,000 feet. Where there is heavy
rainfall and high humidity, as on the Pacific slope and in
the central part of the Magdalena Valley, there are dense
forests, the great trees spreading their branches to form a
canopy far above the forest floor. Within these forests
underbrush usually is not profuse, but at their edges dense
masses of low bushes and intertwined vines compete for
light. Palms—tall species and short ones—throng these
jungles, and many plants have long spines that make
travel uncomfortable. Ferns, cannas, and various banana-
like plants also abound. Sometimes the explorer will find
hunting trails or lumber paths leading into the jungles,
but often he must wade up or down small streams if he is
to penetrate them. Then there are the great arid stretches
where cactuses and acacias thrive. Sometimes, due to a
configuration of the mountains, rain will be shut off from

1. M. Chapman, in an account of the distribution of bird life in Colombia, discusses

at some length the life zones of the country, and his terminology for the different zones
is here used.

[358]

A NEW FIELD FOR BOTANISTS

a very small area, causing an arid pocket in the midst of
a wooded area; such a pocket occurs in the Dagua Valley
of western Colombia. A striking feature of the broad
river valleys are the graceful bamboos lining the stream
banks.

Only a small portion of this rich tropical area has been
explored. Our 1922 expedition entered Colombia by the
Pacific port of Buenaventura, and made extensive collec-
tions about Buenaventura Bay and in the dense and ex-
ceedingly luxuriant forests between the ocean and the
base of the Western Cordillera. This Pacific tropical area
was later explored at a point much farther south, toward
the Ecuadorean boundary, west of Popayan. In con-
nection with the study of the birds of this region Chapman
notes: ““The Colombian-Pacific fauna . . . is one of the
most circumscribed and sharply defined, and possibly the
most strongly characterized of any fauna of South Amer-
ica. Certainly no other area of similar extent in the tropi-
cal zone has so many birds which are peculiar to it.” A
similar statement might be made in regard to the flora.
Of the plants of our collections so far studied a surpris-
ingly large proportion have proved to represent unde-
scribed species.

The subtropical zone extends from the upper limit of
the tropical—which varies between 4,500 and 6,000 feet
depending on temperature and humidity—to an altitude
of about 9,500 feet. In this zone, also, there are dense
forests as well as arid hillsides and plateaus. In these
forests there is nearly always a dense undergrowth, and
the trees and shrubs are literally plastered with a profuse
growth of parasites and epiphytes—orchids, aroids,
bromeliads, mistletoe, mosses, and ferns. The subtropical
ferns are of all kinds, varying from dainty mosslike
“filmies” to large palmlike trees. What is in many ways
the most striking plant in Colombia occurs at the upper
limit of this zone, almost in the temperate zone—the wax
palm of the Quindio trail (Plate 88). It reaches a height

[359]

EXPLORATION IN SOUTH AMERICA

of 200 feet, towering high above other trees, its long
slender white trunk, ringed with black bands and crowned
with graceful foliage, making an unforgettable sight.
Viewing this region from an eminence, one can well ap-
preciate Humboldt’s characterization of it as a forest
above a forest. It is in the subtropical zone that the
botanist finds the most profitable collecting, and much
of the time of the three expeditions has been spent at
these elevations.

Above this zone comes the temperate, reaching to 11,000
or 12,000 feet altitude. The woods here are characterized
by much-gnarled, though usually compact, low trees,
densely covered with moss and lichens. Brilliant fuchsias,
passion flowers, and tropaeolums (our garden nasturtiums)
make a striking display. Here, too, are many plants
familiar to inhabitants of the north-temperate regions—
violets, blackberries, strawberries, mustards, buttercups,
lupines, and asters. One family of plants, the Melastoma-
ceae, only scantily represented in the United States, makes
a fine show of large magenta flowers. Yellow is given to
the landscape by festoons of onciditums and odonto-
glossums (both orchids), and pink by plants of the blue-
berry and lobelia families.

Finally the explorer comes to the paramo zone, the
bleak region lying above timber line. Often the entrance
to a paramo is abrupt; the trail will lead up a gulley
through a growth of stunted trees; a dense foggy mist
will blanket everything; the stream becomes a mere trickle;
and you pass over the edge.

There before you stretches a vast undulating plain,
sometimes broken by domelike rocky eminences. Through
the mist you see a number of tall, straight, dark figures,
the frailejones (little priests), curious wool-clothed plants
related to our sunflower (Plate 90). There are many
kinds of frailejones, some scarcely a foot high, others fully
twelve feet; even the small ones, with their dense rosettes
of leaves, and covered with a thick white or golden-yellow

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A NEW FIELD FOR BOTANISTS

wool, make a striking effect on the paramos. On the
paramo floor are cushions of plants—some are soft moss,
and some have sharp needlelike points, which easily pene-
trate clothing. Of the latter kind are Distichia (Plate
gi), an Andean plant of the rush family, and Aciachne, a
matted grass. Here, too, are plants strongly suggestive
of northern asters, daisies, and black-eyed Susans, though
sometimes the woolly coating of the plant is so dense that
it is difficult to see of what northern plant it is a counter-

art. Gentians—blue, yellow, and white—are every-
where; blackberries and representatives of the heath
family abound. Occasionally a plant of blue-eyed grass,
though usually with a yellow “eye,” is found. For the
most part the ferns are either of the club-moss type or are
stiff straight fronds growing out of a stout rootstock.
There may be depressions or even gulleys in the paramo
where the soil is sufficient to permit the growth of shrubs
or very low trees, and these, sometimes covered over with
fuchsias and passion flowers, add to the general pic-
turesqueness.

So far as is known there is little true paramo in the
Western Cordillera. EF. W. Pennell reached an area of
some five or six acres in the northern part of this range in
1917. In the Central Cordillera the 1917 and 1922 expe-
ditions did extensive collecting on the paramos of Ruiz
and Santa Izabel, respectively. We had hoped to find a
rich paramo vegetation on Mount Puracé, near Popayan,
but this had been almost completely obliterated by thick
layers of ashes from this active volcano. In the Eastern
Cordillera A. C. Smith and the writer, together or sep-
arately, visited ten different paramos.

Such, then, is the general vegetation of Colombia. To
find out what particular species inhabit these zones—
whether they are already known or new to science—in-
volves more than merely passing through the locality and
observing its flora. Descriptions of the known plants of
Colombia are not to be found in a single compact work, as

[ 361 ]

EXPLORATION IN SOUTH AMERICA

are those of many areas in the United States, but are
scattered througha large number of books, which obvi-
ously can not be transported into the wildernesses. Samples
must be taken from the plants, preserved, and brought
back to institutions where facilities are available for their
careful study. It is possible to collect seeds of a few
plants, germinate them in the United States, and make
studies from living material, and sometimes bulbs or
other portions of the plant may be brought back and
grown. But the great mass of taxonomic botanical
knowledge is based upon pressed and dried specimens,
supplemented by notes on the character of the living
plant. Low herbs, of course, can be collected entire, so
that when they are studied a nearly complete picture
of their natural appearance can be had. But of larger
plants, which obviously can not be pressed and dried as
a whole, it is necessary to select portions showing their
essential parts—the flowers, fruit, and foliage.

[ 362 ]

CHAPTER IT
WORK IN THE FIELD

THERE are two main tasks in the making of herbarium
specimens: the actual collecting of the plants, and—as
soon after the collecting as possible—the drying of the
specimens. It is a far cry from the nature lover’s act in
picking a violet and pressing it flat between the pages of a
book to the work of an expedition to the Tropics which
gathers some 7,000 “numbers” in the course of six months.
The cooperative work in Colombia has made necessary the
collecting of three or four specimens of each “number,”
and the gathering and drying of these specimens and the
transportation of the necessary equipment constitute sert-
ous problems. The methods of botanical exploration may
best be illustrated by the description of a typical month
spent by the members of the last expedition to Colombia
in the mountainous region north of Bucaramanga.
Bucaramanga was our principal headquarters in the
Eastern Cordillera. Leaving the greater part of our bag-
gage at a school building placed at our disposal by the
government authorities, we proceeded north to the small
village of California, distant about two days of mule
travel. Here we rented a house and, after making the
necessary calls upon local officials, we were ready to begin
work. Our first excursion was to La Baja, a few miles dis-
tant. This place, indeed, had been the principal factor
in determining to what part of Colombia we should go on
this trip. A mining town of some importance at the
middle of the last century, La Baja had become botanically
famous as the locality at which Linden, Funck, and

[ 363 |

EXPLORATION IN SOUTH AMERICA

Schlim had found a large number of new plants, appar-
ently of limited distribution. Today the town is a mass
of ruins, only three or four houses remaining intact.

The mule trail ascended the La Baja River valley, pass-
ing sometimes through grassy country and sometimes
through deep woods. The equipment which each of us
carried consisted of a pair of pruning shears, a hunting
knife with a saw-toothed edge, and a collecting portfolio,
made of two wooden frames about seventeen inches long
and twelve inches wide, held together by leather straps.
The portfolio contained a number of sheets of white paper
on which to lay the plant specimens.

As this was our first field work in this locality, we col-
lected specimens of every plant that was either in flower
or in fruit. Shrubs were often more easily reached from
the mule’s back, but usually we dismounted to get a
specimen. The specimens were laid in the portfolios,
accompanied by notes on the size and habit of the plants.
When a portfolio became inconveniently full, a situation
which arose every few minutes, we made up a bundle and
cached it beside the trail, to be retrieved on the return
trip.

The leading citizen of La Baja guided us on a short
trip into the mountains, and we made arrangements with
him for a week of collecting later. At the end of the day
we hurried back to our house in California. The bundles
of fresh plants were hung for the night high out of reach
of marauding ants.

There is little advantage in two botanists doing the
actual work of collecting together, so we planned to take
turns in the field, Mr. Smith to spend ten days in the high
mountains to the east while I dried and prepared the
specimens he collected. Then I was to return to La Baja
while he worked at the California headquarters. In the
company of the village priest, whose guest he was to be
at one of the “highest”? towns in Colombia—Vetas—and
of our native helper, Mr. Smith made the steep ascent of

[ 364]

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PLATE 93

La OS a Se.
Preparing plant specimens. Upper: Making bundles for drying.
Lower: Drying plants over oil burners. Photographs by Killip

WORK IN THE FIELD

the Paramo Rico to Vetas. Using this village as a base,
he made daily trips to neighboring paramos. Each
evening the bundles of fresh plants were turned over to an
Indian messenger, who made a moonlight trip across the
mountains to our little house at California. This Indian
packer arrived at about five o’clock each morning, bent
over with a load of some fifteen or twenty small bundles
well lashed together. His pay for the trip—fifty cents—
seemed small recompense.

Each bundle bore a number so that the plants could be
arranged in chronological sequence. The specimens were
unpacked, all dirt washed off the roots, loose flowers or
leaves placed in small envelopes, and each specimen laid
out carefully on clean white paper of standard herbarium
size. Extremely succulent plants were first put in boiling
water to insure quick death and forestall decay while
drying. Next each sheet was given a number and a cor-
responding entry was made in a notebook, giving the
probable generic name of the plant, its habitat, the place
of collection, the coloring of the flower, and a transcript
of additional field notes made by the collector.

A sheet of blotting paper was laid between each pair of
specimens and when a bundle became large enough it
was inclosed between two slat frames and cinched tightly
with web straps. A large part of the moisture in the
plants would thus be absorbed by the blotting paper, and
the next day the specimens were ready for drying over
heaters. For this operation the wet blotting paper was
removed and replaced by dry sheets of blotting paper and
corrugated cardboard in alternation. The packages were
then lashed to the posts and railing of the patio about
three feet above the ground. There are patios, or court-
yards, in all Colombian houses, and they all have posts
or railings. This furnishes an additional reason for doing
this part of the work in a substantial habitation whenever
possible, rather than in a tent. Under each package was
placed a small kerosene stove, and around each bundle a

[ 365 |

EXPLORATION IN SOUTH AMERICA

curtain was draped so that the heat might all pass up
through the corrugated boards and dry the plants more
speedily. Sad experience had taught us the danger of
fires resulting from the curtain being blown into the
flame, so we had constructed protecting shields from ordi-
nary chicken wire, and these were placed around the
stoves.

This drying apparatus required little attention; twice a
day the bundles were reversed and the stoves refilled. The
length of time needed to dry plants obviously depends on
the nature of the individual plants. Ferns, grasses, and
slender herbs will usually dry within twenty-four hours;
most plants will dry within forty-eight hours; orchids,
aroids, cacti, and similar fleshy plants may require as long
as a week to dry thoroughly. Fortunately kerosene is
obtainable at all important places in Colombia, though
at exorbitant prices in regions where the cost of trans-
portation is high. However, we have found no satis-
factory substitute. Charcoal was used on one trip but
the difficulty of maintaining an even heat led to several
destructive fires, one of which required the summoning of
the entire village fire department to save the building; as
a further disadvantage, charcoal makes necessary the
continued presence of a man to feed fuel. The kerosene
stoves, on the other hand, require no attention for twelve-
hour intervals. It is, of course, possible to dry plants
without artificial heat by changing the blotting paper
repeatedly and drying the wet paper in the sun or near a
stove. But this method is slow and is scarcely practicable
when large collections are being made. We averaged 150
collecting numbers, or about 400 individual specimens,
a day.

Once the plants are thoroughly dried they are made into
small packages and are ready for shipment to the United
States. A quantity of naphthaline is placed with the
specimens to prevent molding.

The collecting and drying of plants at the little Colom-

[ 366 |

WORK IN THE FIELD

bian town of California was done under ideal conditions.
When a long journey by mule through a sparsely settled
country is undertaken additional problems arise. If an
expedition moves over a trail rapidly to reach at night a
satisfactory domicile where adequate preparation of the
specimens can be made, it will overlook many rare plants
en route. If the party moves slowly, collecting abundantly,
camp may have to be made at a point where the material
can not be well assorted and dried. We usually traveled
slowly, collecting all but the most common plants. At
night we laid the specimens between driers, changed the
driers the following day, and then, when a satisfactory
stopping place was reached, spent three or four days in
drying the specimens over the heaters.

The equipment for a six months’ botanical trip is neces-
sarily large. In addition to the usual articles such as
tents, folding cots, hammocks, cooking utensils, mosquito
netting, common tools, and medicines, we took as special
equipment for the botanical work 15,000 sheets of white
paper of standard herbarium size, 2,500 sheets twice as
wide and folded once lengthwise, 1,800 sheets of blotting
paper, 700 corrugated cardboards, 20 wooden frames to
serve as press ends and an equal number of web straps, 3
collecting portfolios, 5 kerosene heaters with curtains to
drape about them, several pounds of naphthaline, pruning
shears, ASL on Ie and sundry articles such as twine, rope,
and tags.

To the parts of Colombia visited by the recent expedi-
tions it is unnecessary to carry large quantities of pro-
visions. In the mountains bread and cheese, chickens and
eggs, meats, potatoes, and sweets may be obtained nearly
everywhere, and, of course, in the lowlands a great
variety of food can be had. The main problem in the
matter of provender is pasturage for the mule caravan; and
frequently the stopping place of an expedition is deter-
mined not by the rare botanical specimens available but
by the common fodder crops for the mules.

[ 367 |

EXPLORATION IN SOUTH AMERICA

Our equipment was packed in twelve light but strong
fiber cases two and a half feet long, one and a half feet
wide, and one foot deep. This size is well adapted to the
economic packing of the paper supplies, and, moreover,
such cases are easily adjustable to a mule’s back.

Nearly all travel in the Colombian mountains is done by
horse or mule—the horse for the more dignified voyager
on the well-beaten roads, the mule for cargo and the less-
used trails. Although agencies will transport baggage at a
variable rate, often quite high, a better method is to pur-
chase the mules or to rent them by the week or month,
engaging a muleteer, or arriero, to have charge of the
loading and driving of the caravan. Two fiber cases are
secured to each mule by an elaborate system of roping,
during which cloth is placed over the animal’s head lest
he take fright and run. The arriero well appreciates the
need for care in this loading, for if the pack should become
loose and unbalanced, the mule might easily slip over a
precipice, and mule and cargo be permanently lost.
Often on the road the pack slips and then the muleteer
hastens to throw a cloth over the mule’s head and adjust
the cargo. At night the good arriero never thinks of rest-
ing or of eating until the mules have been unloaded, their
backs massaged, and the animals led to pasture—often a
long distance from the inn.

The complex task of drying specimens makes a sub-
stantial headquarters for the night almost a necessity, and
consequently tenting has been avoided on these botanical
trips as far as possible. In the larger cities that served
as main bases, the local authorities generously placed at
our disposal some public building, which served as work-
shop, storehouse, and eating and sleeping quarters in one.
In Popayan the building given us had formerly housed a
convent. It was a beautiful two-storied example of early
Spanish-American architecture with large patios. Com-
fortable beds had thoughtfully been provided; meals were

served in a spacious dining room; and a reception room

[ 368 |

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PLATE 95

A caravan of mules arriving at Popayan, Colombia. Photograph
taken from the expedition’s headquarters by Killip

WORK IN THE FIELD

had been set apart, to which the important citizens came
immediately on our arrival with every offer of assistance.
In Bucaramanga we were given a nineteen-room school
building. In Salento, as in California, we rented a house.
In a few large cities we lived at hotels, though the inter-
ruption our work offered to the normal quietness of these
more pretentious hostelries was not always welcome.
Rooms in a modern flour mill at Surata, a village near
California, were given us free of charge. At La Cumbre,
on the crest of the Western Cordillera, in a region un-
usually rich in dense vegetation, quarters were found in an
American hospital. Several times hunting lodges in
virgin wilderness were turned over to us by their generous
owners.

Often, especially on long trips, we stopped at any inn
or hut which might conveniently come into view about
three o’clock in the afternoon. Considerable persuasion
was frequently necessary to gain permission to remain if
the spot were not a regular stopping place for distin-
guished caballeros. Though a caravan of cargo mules
might well have arrived there already, the innkeeper,
usually a woman, would protest that she had not the
right kind of food for such as we and that certainly we
would not wish to crowd into the one room already occu-
pied by several muleteers. Once we suggested that we
sleep on our cots on the porch; a horrible suggestion, ap-
parently, for, she protested, “You will die. The night air
is filled with disease and evil spirits.” And when in the
morning she found us still alive, it was hard to say whether
relief that we were not dead or chagrin at the nonfulfll-
ment of her predictions predominated.

Our full complement of baggage required six mules, and
the loading of these in the morning took much time. My
companion and I usually started off on the trail well in
advance of the cargo, and, traveling slowly, we made a
thorough job of collecting. In time the cargo caravan
caught up with us, and then inevitably much confusion

[ 369 |

EXPLORATION IN SOUTH AMERICA

ensued as the burdened animals tried to pass our riding
mules; for the Andean mule is a wise beast and has
learned always to strive for the inside track on the narrow
trails where a misstep on the outside track means a
plunge over a precipice. To the already well-laden mules
we would add our morning’s collections and allow the
caravan to pass on to a satisfactory halting place for
the night.

In the lowlands travel by mule is supplementary to
travel by boat, railroad, and auto. The two main arteries
of Colombia are the Magdalena and Cauca rivers, though
neither is navigable its entire length and detours must be
made around rapids. The boats are oil-burning or wood-
burning side-wheelers and on the whole quite comfort-
able. The few staterooms are usually reserved for women
passengers, the men sleeping on cots on the decks. Oil-
burners are preferable because their stops for fuel are in-
frequent. Small gasoline launches or canoes can be used
profitably by the botanist for the exploration of coastal
strips and river valleys. Skirting the low shores of
Buenaventura Bay or Cartagena Bay in a canoe gives a
wonderful opportunity to collect interesting plants. The
natives climb the overhanging trees and throw into the
canoe rare orchids, aroids, and bromeliads. Only by
canoes may the narrow water passages among the man-
groves be explored.

The heavy seasonal rains and the loose, shifting charac-
ter of the soil often cause the destruction of long stretches
of railroad and highway. The fine new road along the
Pamplona Valley from Pamplona to Cicuta, which we had
planned to take toward the end of our last trip, was out of
service, some portions of it nearly a mile long having been
washed into the river. So we were obliged to flounder
through a muddy “‘washerboard”’ trail, once abandoned.
The night before we planned to go from Buenaventura
to La Cumbre, in the Western Cordillera, landslides had
blocked the railroad at several places. The train steamed

[ 37° |

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WORK IN THE FIELD

to the first blockade, waited till the débris had been re-
moved, then went on to the second. At one obstruction,
too great to be cleared away in a day, the passengers were
transferred to a small flat car and an exciting ride ensued,
two natives pushing the car to the top of a grade, then
letting it race madly down the winding track at the edge
of the gorge, with no brake other than a crowbar pressed
against a rapidly revolving wheel. With the development
of modern means of transportation in Colombia, as well
as in other South American countries, the work of the
botanical explorer will be greatly simplified. Less time
will be consumed in reaching the area to be explored;
equipment can be transported more safely; and the speci-
mens collected can be shipped out with a greater chance of
eventual arrival in the United States.

ExpLorinc BEYonD THE PERUVIAN MounrtTaAINS

From Colombia the Andes extend for nearly 4,500
miles almost to the southern tip of the continent, a great
mass of mountains, many of them snow capped, cleft here
and there by passes through which travel moves into the
interior. The proximity of the cordillera to the ocean has
resulted in a curious, uneven development of these western
countries. Cities have sprung up on the coast or on the
nearby mountain slopes, where trade with the outside
world might more easily be carried on. Other cities have
grown up in the cooler, more invigorating climate of the
higher altitudes. Caravans of trade have passed from
the mountains to the coast and from the coast to the
mountains. But across the mountains was another world,
a world seldom or never visited. Roads leading to it, even
the narrowest of mule trails, were few. The friendliness
of the native Indian tribes was uncertain, and living
conditions were of the most primitive sort. Here and
there outposts of civilization were established, mainly
along the most direct routes from the mountains to the
navigable portions of streams flowing toward the Atlantic,

[371]

EXPLORATION IN SOUTH AMERICA

and along the Amazon and its larger tributaries. But
even today there are vast, almost wholly unexplored
regions in southeastern Colombia, eastern Ecuador,
northeastern Peru, eastern Bolivia, and northeastern
Chile. All this eastern country is known as the montana.
Most of it is dense forest, though in Colombia there are
long stretches of grassland. Rainfall is heavy, though
usually there are two well-marked seasons, a dry one and
awetone. Travel is by canoe, by river steamer, by mule,
and in recent years by airplane.

From Callao, the principal seaport of Peru, and Lima,
the capital, seven miles inland, the main route of travel to
the Amazon runs almost due eastward over the cordillera
to the Chanchamayo Valley, then northeastward over a
lower, rather isolated range of mountains to the Pichis
River, down this and the Pachitea to the Ucayali River,
which unites with the Marafién, coming from the west,
to form the Amazon. The first part of the trip, from the
coast to the Chanchamaypo, is by rail and auto, the rail-
road crossing the crest of the Andes at an elevation of
15,600 feet, a marvelous feat of engineering with over
sixty tunnels, numerous “switchbacks,” and high bridges.
From Oroya, in a valley between the main ridge and the
lower, Eastern Cordillera, the route continues by an auto
road over this second range, then down to San Ramon,
La Merced, and the Perené Colony, the three most im-
portant places ; in the Chanchamayo Valley.

This descent from 14,000 feet to 2,000 feet is full of
thrills, most of the “drop” coming within a few miles.
The road is scarcely wider than the car and consequently
for the greater part of the route one-way traffic is main-
tained, cars descending three days a week and ascending
on alternate days. Looking ahead the road seems so
narrow at places that no car can pass, but it does, scraping
the jutting rocks on the inside, the wheels perilously near
the outer edge. A tunnel looks like a rabbit hole—much
too small for the car to enter. But you pass through

[372]

WORK IN THE FIELD

safely, the top of the car brushing against the roof of the
tunnel. By nature these Latin-American drivers are
thrill-loving, and they make more use of the accelerator
than of the brake.

At the end of the highway you have a choice of con-
tinuing your route to Iquitos on the Amazon by air, a
day’s flight, or by land, a three weeks’ trip. The air
journey, though, of course, impossible for the botanical
collector, gives a wonderful view of the vast rolling
Amazonian forest, streaked with the crooked silvery lines
of the rivers as they make their way, steadily growing
broader, to the great river. The aviators in this service
relate many an adventurous tale of forced landings on
river banks in the heart of the wildest Indian country,
their planes bearing the marks of hostile arrows.

Few parts of Peru are more interesting to the botanist
than the Pichis trail, the only portion of the land route
from Lima to the Amazon that must be made by mule.
Much of this is through subtropical forest between 5,000
and 6,000 feet elevation, and there is a constant change
of vegetation from day to day. Color is given to the
forest by red fuchsias, blue monninas (a shrub related to
our northern polygalas), and yellow composites. Hidden
in the jungle we found an open sphagnum swamp, much
like those of our Northern States but with only one
familiar species, the cinnamon fern.

One of the pleasant features of this trail is the presence
of delightful ambos, or inns, at the end of each day’s
journey. Flimsily constructed though they are, and with
domesticated animals ever present, sleeping accommoda-
tions are satisfactory and the meals remarkably good.

At Puerto Yessup canoes are boarded. How far one
must travel by canoe depends on the depth of the water;
steam launches do not go far up the Pichis River in the
dry season. Canoeing down these small streams is a
fascinating experience. The banks are close enough to
permit the recognition of individual trees. In the pro-

L373)

EXPLORATION IN SOUTH AMERICA

fusion of vines, morning-glories, passion flowers, and plants
of the pumpkin and grape families predominate. On the
broader rivers the shore appears merely as a dark band
between the sky and the water. Animal life, too, seems
more abundant on the smaller streams. Gorgeous par-
rots and macaws fly screeching overhead; alligators and
giant turtles bask on the beaches; monkeys swing from
tree to tree, howling uncannily. Many times canoeists
must disembark in the middle of the river to drag the
boat over shallow stretches. Often the water is so swift
that there is danger of an upset.

At length one reaches a point where navigation by
larger boat is possible, and one steams slowly onward,
day after day, down the Pachitea and Ucayali rivers till
the Amazon is reached. These boats are wood-burners,
and much time is consumed taking on wood. At con-
venient spots on the banks are great wood piles, and hour
after hour there is a continuous procession of slow-moving
natives carrying the logs to the ship. Stops may be made
for the loading of cattle, cotton, or bales of balata, one
of the rubber plants of the upper Amazon country. Many
of these boats are trading ships, carrying a large assort-
ment of goods to be sold to the natives or, more usually,
exchanged for local products, each transaction accom-
panied by the customary tedious bargaining.

From the base of the Andes to the northern and eastern
boundaries of Peru and across into Ecuador and Brazil
there lies the vast, almost unbroken forest, penetrable
only by the rivers and the narrow trails which connect
the more important settlements. Here and there is an
Indian chacra, a hut or two about which a clearing has
been made for the growing of yuca (cassava), bananas,
platanos, and barbasco. The first three are the main food
products of the natives, and the barbasco is used in
fishing. But for mile after mile there is nothing but
forest.

The number of different species of plants within a given

[ 374]

WORK IN THE FIELD

area is almost beyond estimate; certainly it is many times
greater than in a similar area in a northern woods. Col-
lecting herbarium specimens to represent even a fair
number of these plants is no easy task. Often the desired
flower or fruit towers high above the collector’s head, to
be reached only by an arduous climb up through the
entanglement of vines at the river’s edge. Back of this
network are the trees, trees of all sizes from small shrubs to
giant ceibas and mimosas, all bound together by lianas
and covered with a dense epiphytic growth of orchids,
bromeliads, ferns, and mosses. To get specimens from
many of the trees means cutting down the tree. Often
merely cutting through a trunk does not fell an Amazon
tree, for the upper part may be held up by the lianas or
it may lodge on another tree, which in turn has to be
cleared away. The natives are adept climbers and often
go up a tree trunk or a swinging liana to get the speci-
men. Sometimes in the less dense forest a branch of
flowers may be shot off. Naturally, however, the greatest
hauls are made at recent clearings. Often while walking
along a trail we would hear the sound of an axe, make for
it, and there where some Indian was making his home in
the virgin forest spend profitable hours among the fallen
treetops. An added advantage of collecting under such
conditions is that the native usually volunteers informa-
tion about the plants—the quality of the various timbers,
the effectiveness of different drugs.

Even after they are collected, the specimens require
much attention to forestall the attacks of ants and other
insects, and of mold. A package of specimens left on the
floor at evening will by morning have great ants’ nests
between nearly every pair of paper sheets. The general
dampness of the Amazonian forests hastens the decay of
specimens so that they must be cared for immediately,
and, when dried, well sprinkled with naphthaline. All
this attention, of course, is necessary anywhere in the
Tropics but it is particularly so in the Amazon country.

[375 ]

EXPLORATION IN SOUTH AMERICA

Our almost complete lack of knowledge of the upper
Amazon is amazing. One of the most commonly culti-
vated plants in northeastern Peru is the darbasco, or cube,
the roots of which are used by the natives to stupefy
fish; yet until recently its botanical name was not known,
and apparently no specimens of it were to be found in
American herbaria. This plant will doubtless have
great commercial value as an insecticide. Another plant,
ayahuasca, or caapi, used by the Indian medicine men to
produce fantastic dreams, is a strong narcotic, possibly of
great medicinal value; yet, it, too, is almost wholly un-
known outside of its native haunts. And who has heard of
the abuta or of the chuchuhuasca, two other cure-alls of
the natives? What other plants are hidden in the dark
recesses of this Amazon country or in the mountains to
the westward that might prove of great commercial
value? What gorgeous flowers that might be brought to
horticulture? What fruits that might find their place
beside the banana, the orange, and the avocado?

[ 376 |

SELECTED BIBLIOGRAPHY

CuapMan, Frank M. The distribution of bird-life in
Colombia; a contribution to a biological survey of
South America: Amer. Mus. Nat. Hist. Bull., Vol.
oon iNew Lork, No17:

GarDNER, GeorGE. Travels in the interior of Brazil.
London, 1846.

Miers, Joun. Travels in Chile and La Plata. London,
1826.

ScHOMBURGH, RicHarp. Botanical reminiscences in
British Guiana. Adelaide, Australia, 1876.

Spruce, Ricuarp. Notes of a botanist on the Amazon
and Andes. London, 1908.

WALLACE, ALFRED RUSSELL. A narrative of travels on the
Amazon and Rio Negro, with an account of the
native tribes and observations on the climate,

geology, and natural history of the Amazon Valley.
London, 1853.

[377]

Absorption by plants, 297-300

Abuta, 376
Acetabularia, 178
Achiachne, 361
Acorns, 116

Adaptations, 32, 33, 55-59, 78-80,

255, 279-281, 291
Aegilops, 232
Agar-agar, 89, 184
Agriculture, 319-324
Agropyron, 20g, 225
Agrostis, 234
Alaria, 184, 186
Alders, 117
Algae, 87-89, 167-197
bibliography, 197
blue-green, 175, 177, 178
brown, 175-177
classification, 175
color, 175
coralline, 180
distribution, 169, 170
environment, 168-172
filamentous, 88
food of, 170, F971, 373
fossil, 195
fresh-water, 175
green, 175, 177, 178
iodine absorbed by, 187
marine, 175
motile spores, 72
protective devices, 173
red, 175, 178-180

relation to animal life, 187-192

reproduction, 173, 174

INDEX

Algae, seasonal abundance, 170
structure, 168, 171-174
uses, 184-196

“Alkali” concentration, 11

Amaranths, 117

Amaryllis family, 114

Ammophila, 227

Andropogon, 246, 249, 342

Andropogoneae, 341

Angiosperms, 94-96

Anther, 41, 43

Apetalous plants, 117, 118

Aquiculture, 185, 186

Aralia family, 126

Aristida, 246, 248

Aroids, 113

Arrowhead family, 112

Arrowroot family, 114

Arundinaria, 248

Arundo, 235

Aster family, 129, 130

Avena, 210

Ayahuasca, 376

Bacteria, 27, 28, 38, 89, 90
diseases caused by, 89, go
multiplication, 90
nitrogen fixation by, 27, 28
reproduction, 38

Balsam family, 122

Bamboos, 229, 235

Bambus, 229

Bananas, 114

Barbasco, 376

Bark, 12-14

[379 ]

INDEX

Barley, antiquity, 209
Barley grasses, 232
Basswood, 123
Batrachospermum, 175
Beach grass, 227
Beans, dispersal, 55, 56

germination, 60, 61
Beeches, 116
Bees, relations to flowers, 51, 52
Begonias, 125
Bent grasses, 234, 235
Bermuda grass, 222, 235
Beverages from plants, 101, 109
Bibliography, 111

of desert plants, 284

of field work, 377

of grasses, 250

of maize, 349

of radiant energy and plants,

315

of sea plants, 197

of systematic botany, 164
Billion-dollar grass, 225
Birches, 117
Bladderwort, carnivorous habit,

75
Bluebells, 129
Bluegrass, 221, 222, 234
Botany, ancient, 134-138
defined, 1
economic, 2
“German Fathers of,” 139
modern, 142
of the Renaissance, 138-142
origin, 133
primitive, 133
specialization in, 161
systematic, 2, 133-164
bibliography, 164
future, 161-163
methods, 149, 150, 153-155
taxonomic, 133-164
three phases, 1
Bougainvillea, inflorescence, 118

Boyce Thompson Institute, 303,
306

Branches, functions, 3

Brandes, cited, 212

Bread mold, spores, 39, 40

Breasted, quoted, 204, 207, 209

Breathing pores of leaves, 24, 25

British Museum, herbarium, 150

Brome grasses, 232

Bromeliads, 114

Bromus, 232

Bryophyta, 93

Buckeyes, 122

Buckwheat family, 117

Budding, propagation by, 69

Bud scales, function, 20, 21

Buffalo grass, 244

Bulbs, propagation by, 64, 68

Bunch grasses, 244, 245

Buttercups, 118, 119

Caapi, 376
Cacao tree, 123, 124
Cactizona, 125
Cactus, barrel, 274, 278

families allied to, 126

tree, 278

uses, 125
Cactus family, 125, 126
Calla lily, 113
Calyx, 41
Cambium, 12-14
Canary grass, 248
Candolle, A. P. de, 144, 308, 309
Cannas, 114
Carbohydrates, 26, 27, 289-294
Carbon dioxide, 26-29, 300
Carboniferous Period, 94
Carnivorous plants, 72-76
Cashew family, 122
Cassava, use, 121
Castor-oil plant, 121
Catchfly, sticky secretion, 75

[ 380]

ot >

INDEX

Catkins, 116, 117
Cat-tail family, 112
Cells, reproduction, 38
structure, II, 12
Cenchrus, 230
Cereals, domestication, 325
Ceriman, climbing, 113
Chenopods, 117
Chestnuts, 116
Chlorophyll, absent from parasitic
plants, 30, 31
as catalyzer, 289, 290
defined, 8
function, 26, 189, 190
in algae, 187, 188
two kinds, 290
Chlorosis, 8, 9
Chocolate, source of, 123
Chondrus, 184
Chroococcus, 178
Chuchuhuasca, 376
Cilia, movements, 72
Citronella grass, 230
Citrous fruits, 121
Citrus, 121
Civilization, and agriculture, 319
and grasses, 201-215
Clambering by plants, 34
Classification, 143-145
of algae, 175
of grasses, 241, 242, 248, 249
systems, 130, 143-148, 153
Climbing plants, 33-37
Clover in crop rotation, 28
Club mosses, 94
Coconut palm, uses, 113
Coleoptiles, 310, 312
Collins, cited, 214
Colombia, botanical exploration,
303-372
topography, 356
vegetation, 357-362
Colors of light, 292
Composites, 130

Conifers, 94

Copra, 113

Coracan, 211

Corallina, 179

Corallines, 179

Cordus, V., 139-141

Corms, propagation by, 64, 68

Corn, Indian, see Maize

Corolla, 41

Cortaderia, 235

Cotton, economic importance, 123

Cotyledon, 60

Crop rotation, 28

Cross, between varieties, 53

Cross-pollination, 43, 44, 46, 52,
53

Crosses, propagation, 53, 54

Crucifers, 119

Cube, 376

Cuttings, propagation by, 66, 68,
69

Cycads, 95

Cynodon, 235

Dandelion, propagating roots, 65
Darwin, C., 145
on pollination, 43, 44
Dasya, 178
Deserts, and plants, 255, 264-281
atmosphere, 261
bibliography, 284
climate, 255-262, 277
evaporation, 256-258, 282, 283
extent,.263, 264
lakes, 263
pavement, 262
radiation, 261, 262
rainfall, 256-258, 274-279, 282,
283
soil, 262, 263
temperature, 258
water supply, 256
wind action, 262, 263

[ 381 |

INDEX

Diatomaceous earth, 87, 88, 192-

196
Diatoms, 87-88, 168, 180-183,
192-196

abundance, 183
and animal life, 190, 191
antiquity, 183
distribution, 182, 183
fossil, 192-196
locomotion, 181, 182
reproduction, 182
structure, 180
Dicotyledons, 95, 96, 116-130
apetalous, 117, 118
germination, 60-63
Diffusion through plant cells, 29
Digestion by plants, 28
Digitaria, 211
Diseases, caused by bacteria, 89,
go
caused by fungi, 91
Dispersal of plants, 55-59, 82,
118, 124
Distichia, 361
Distribution of plants, 80-85
Dodder, 30, 31
Dogwood family, 126
Douglass, A. E., on tree rings, 15,
16
Drugs from plants, 100, Io1, 108
Drying plants in field, 365, 366
Duckweeds, 113
Dulse, 185
Dunes, movements, 226
Durra, 211
D’Urvillaea, 175, 176, 184
Dyes from plants, 103, 109

Ebony family, 127
Echinochloa, 204, 225
Ecology defined, 78
Economic plants, 98-130
Felgrass, 168

Eleusine, 211
Elm, arrangement of leaves, 18, 19
Elms, 117
Embryo plants, 42, $9, 60
Emerson, quoted, 168
Emmer, head, 207
wild, 207
Endlicher, 144
Engler and Prantl, on classifica-
tion, 130
on flowering plants, 96
English rye grass, 222
Environment, adaptations of
plants to, 78-80
Enzymes, function, 29
Epicampes, 229
Epidermis, of leaf, 24
of stem, 12, 14
Epiphytes, 79, 114, 115
Eragrostis, 211
Erianthus, 235, 246
Etiolated shoots, phototropism,
12
Euchlaena, 214, 331, 333-344
relation to maize, 331, 335-344
Eulalia, 235
Evaporation from plants, 25
Evening primrose, pollination, 126
Evergreens, 94, 95
Evolution, theory of, 145-147
Expedition, North Pacific, 151
to south America, 355
U. S. Exploring, 151
Explorations. botanical, 160, 353-
376
in South America, 354-356
bibliography, 377
in tropical America, 353

“Fairy rings,” 244, 245
Farlow, quoted, 145
Fermentation, 89
Ferns, 86, 93, 94, 267

[ 382 ]

INDEX

Fertilization in plants, 39, 41, 53
Fescue grass, 248
Fibers from plants, ror, 102, 109
Field work, see Plant collecting
Figwort family, 128

plants allied to, 128
Filberts, 117
Flower, structure, 41
Foods from plants, 98-100, 104-108
Forage grasses, cultivated, 222-226
Fountain grass, 235
Frailejones, 360, 361
Frogbit family, 112
Fruit and seed, 43
Fruits, winged, 56
Fungi, 87, 89-93

Gametophyte, 268

Gamma rays, 288

Garner and Allard, on photo-

periodism, 303, 304

Gelatins from algae, 187

Generations of plants, 267, 268

Geotropism, 63

Germination, 59-62, 60-63

Giant reed, 235

Gigartina spinosa, 185

Gingers, 114

Girdling of trees, 14, 15

Glacial epochs, 83, 84

Glucose, 289

Goat grass, 232

God grass, see Teosinte

Goosefoot family, 117

Gourd family, 62, 129

Gracilaria, 184

Grafting, 69-71

Grama grasses, 244, 245

Gramina, 203

Grapes, 71, 122, 123

Grass, leaves, 201-203
seed, as food, 204
spikelets, 240, 241

Grasses, 201, 250
and civilization, 201-215
and wealth, 216-237
antiquity, 203
as land builders, 226-229
barley, 232
bent, 234, 235
bibliography, 250
brome, 232
bunch, 244, 245
classification, 241, 242, 248, 249
decorative value, 232, 234-237
dispersal, 245, 246
distribution, 242-244
economic importance, 216, 217
flowers, 238-241
forage, 218-226
fossil, 241
germination, 247, 248
grama, 244, 245
growth, 201-203
heads, 208
injurious, 230-232
lawn, 234, 235
longevity, 244
marsh, 227-229
ornamental, 235-237
plants related to, 242
pollination, 240
products from, 217, 218
reproduction, 215, 340, 341
structure, 238, 239
tribes, 248
turf, 235
Uses) 217—226,/229, 230
vegetative propagation, 244, 245
villainous, 231, 232, 234
Grass family, 112
“Great millet,” 211
Greene, E. L., quoted, 135, 138
Greenhouse, use, 149
Griggs, R. F., cited, 175, 186
Guppy, H. B., cited, 85
Gymnosperms, 94, 95

[ 383 |

INDEX

Halophytes, 78, 79

Hay, 222, 229, (205

Hazelnuts, 117

Heath family, 126, 127

Heliotropism, 32

Herbarium, specimens, 365, 366
USe, 149) 150,15 3—1 55

Heteropogoi, 230, 231

Hickories, 117

Hoagland, D. R., on Nitella, 298,

299

Honeysuckle family, 129

Hordeum, 209, 232

Horsechestnuts, 122

Horticulture, 52

Hortus siccus, 149

Huxley, 145

Hybridization, 53

Hydrophytes, 78

Hystrix, 237

Ibervillea, 278, 279

Iceland moss, 93

Ichu grass, 230

Ilex family, 122

Indian corn, see Maize

Indian rice, 215

Insects, relation to plants, 51

Introduction of foreign plants, 160

Iodine, from kelp, 186, 187
in sea plants, 173

Tridaea, 184

Iris family, 114

Irish moss, 184

Iron in plants, 8, 9

Irrigation, excessive, II

K
Kafir, 211
Kao-liang, 211
Kelps, 88, 168, 185, 186

L
Lady’s-slipper, 47, 49, 115

Laminaria, 184
Land building by grasses, 226-229
Landsburgia quercifolia, 176
Laurel family, 118
Laurencia pinnatifida, 185
Leaves, 22-27
arrangement, 17-19, 23, 32, 33
development, 16, 17, 20, 21
functions, 3, 22, 23, 26, 27, 269
modifications, 19, 271-273
relation to light, 32, 33
scars from, 22
separation from twig, 21, 22
structure, 23-25, 113, 118
water absorbed by, 30
Legumes, 27, 28, 120
plants allied to, 120, 121
Leguminosae, 27, 28
Lessonia, 176
Lichens, 91-93
Light, 287
effect on plants, 26, 32-37, 292,
298, 299, 301-306, 313, 314
Lightning, effect onatmosphere, 27
Lily, bulb, 68
structure, 41
Lily family, 114
Limetree, 123
Linden, 123
Lindley, on passion flowers, 124
Linnaeus, 142-144
Lipoids, 276
Lobelias, 129
Lolium, 222
Longfellow, quoted, 185
Loosestrife, winged, 10
Lygeum, 229

M
Mace, 118
Macrocystis, 176, 186
Madder family, 128, 129

[ 384 ]

INDEX

Magnolias, 118
Maize, 213, 214, 319-348
antiquity, 213, 324, 326, 327
bibliography, 349
classification, 330, 331
colors, 327, 328
cultivated by Indians, 213, 214,
346
development by selection, 342
distribution, 346
ear, 336-340
germination, §9, 247, 248
importance, 325, 346, 347
in art, 346, 348
in Mexico, 330
in Old World, 347
in Peru, 330
legend, 213
mutations, 344
origin, 214, 329-348
peculiarities, 325, 326
relation to Andropogoneae, 341,
342
relation to Euchlaena, 336-341
similarity in type, 345
tassel, 337
variability, 345
wild relatives, 331-335
Mallow family, 123
plants allied to, 123, 124
Mammoth tobacco, 304
Mangrove, 10, 54
Manometer, 5, 6
Maple, arrangement of leaves, 18,
19, 54, 62
Maple family, 122
Marram-grass, 227
Marsh grasses, 227-229
Mastophora, 179
Melastomaceae, 360
Melica, 237
Meristem tissue, 311
Mesophytes, 78-80
Metabolism in plants, 28, 29

Migration of plants, 82-85
Mildews of plants, g1
Millet, antiquity, 204, 211
varieties, 211
Milo, 211
Mimosa, movements, 72-74
Mint family, 127, 128
Mints, pollination, 127, 128
Miscanthus, 235
Mistletoe, 30
Monocotyledons, 95, 96, 112-116,
242
germination, 60
Monstera, 113
Moore, Thomas, quoted, 169
Morning-glory family, 127
Morong expedition, 355
Mosaics, leaf, 19, 33
Mosses, 86, 93
Movements of plants, 72-74, 181
Mulberries, 117
Mummy wheat, 209
Mushrooms, cultivation, 92
Mustard family, 119
Mutation, 343-346
Mycelium of fungus, 92
Myrtle family, 126

Nectar of plants, 47, 51, §2

Nereocystis, 175, 186

Nettles, 117

Nightshade family, 128

Nitella, bromine absorbed by, 298,
299

Nitrogen fixation, 27, 28, 89

Nodules of legumes, 27, 28

Nomenclature, 143, 162

North Pacific Exploring Expedi-
tion, I§1

Nutmeg tree, seed dispersal, 118

Oak, germination, 61

Oaks, 116

[385]

INDEX

Oat, wild, 210
Oats, 210
Odors of plants, 47
Offsets, propagation by, 64, 68
Oil, in diatoms, 195
in seeds, 42
Olive family, 127
plants allied to, 127
Opuntia, 260, 278
Orchard grass, 248
Orchard trees, pollination, 52, 53
Orchids, 115-116
Organic compounds produced by
plants, 26, 27
Oryza, 210
Osmotic pressure of sap, 275, 278
Ovary of flower, 41
Ovules, 41, 42
Oxygen, absorbed by plants, 28
released by plants, 27

iP.

Palms, 112,013, 359,.360

Pampas grass, 235

Panicum, 211, 236, 237, 249

Paper from grasses, 229

Papyrus, 112

Paramos of Colombia, 361

Parasitic plants, 30, 31, 288

Parsley family, 126

Paspalum, 225, 249

Passion flowers, 124

Pasteur, on putrefaction, 90
on rabies, go

Pasture, 220-226

Pea, germination, 60, 61

Pea family, 120

Peanuts, 120

Pears, Bartlett, pollination, 52, 53

Peat, 93

Pennisetum, 211, 235

Peppermint, rootstocks, 64

Peru, vegetation, 376

Peruvian winter grass, 226

Petaliferous plants, 117, 118
Petals, 41
Phalaris, 226
Phlox family, 127
Photometer, plant, 314
Photoperiodism, 303, 304
Photosynthesis, 26, 27, 289-295
Phototropism, 307-313
Phragmites, 246
Pigweed family, 117
Pineapple family, 114
Pink family, 118
Pistil, 41
Pitcher plants, 75, 76
Pith of stem, 12, 14
Plant cells, 11, 12, 29, 38
Plant chemistry, 27-29
Plant collecting, 363
bibliography, 377
methods, 365, 366
in Petrus $3743. 375
Plant life and radiant energy,
287-314
bibliography, 315
Plant photometer, 314
Plant societies, 77-85
Plant specimens, labeling, 153
preparation, 153, 365, 366
preservation, 149, 150
types, 15$-157
Plantain, use as food, 114, 115
Plantains, 128
Plants, absorption by, 28, 297-300
adaptations, 10, 32, 33, 55-59,
78-80, 255, 265, 271-279
and “alkali” 11
and heat, 260
and insects, $1
and light, 32
and man, 2
and radiation, 288
and solar energy, 293-295
and water, 9, 11, 30, 269, 273,

“Ihe

[ 386 ]

Plants, apetalous, 117, 118
bibliography, 111
carnivorous, 72-76
classification, 2, 86
climbing, 33-37
crossing, 53
cultivation, 10, II, 53
desert, 264-270
digestion by, 28
dispersal, 55-59
distribution, 80-85
domestication, 320, 324
economic, 98-130
embryos, 42, 59, 60
evaporation in, 269
extermination, 80
fertilization, 39, 41
flowering, 31, 40, 41, 60-63
food of, 6-9, 296, 297
generations, 267, 268
green, 289

growth, 32-37
hybridization, 53

in sleeping rooms, 28, 29
introduction, 160
irrigation, II

life cycle, 267

marine, 180
metabolism, 28, 29
migration, 82-85
movements, 72-74, 181
nervous system, 74
nonflowering, 31

of Peru, 376
one-celled, 38

organs, 2, 3, 38
parasitic, 30, 31
petaliferous, 117, 118
phototropism, 308
physiology, 1, 2
primitive, 266
protective devices, 75

relationships, 86-96, 112-130

reproduction, 38-71

INDEX

Plants, sea, 167-197
sex, 266, 267
source of organic compounds,
20527
specialized, 29, 30
Structure, 274-279
suction power, 278
uses, 97-110
vascular system, 22, 23
without chlorophyll, 31
Plocaria, 185
Plume grass, 235
Plumule, 41
Poa, 234
Poison ivy, 122
Poison oak, 122
Pollen, 41-51
germination, 41, 42
transportation, 44-51
Pollen tube, growth, 41, 42
Pollination, 43-55, 114, 124, 126-
128
Pondweed family, 112
Pondweeds, 30, 112
Poplars, 116
Pores of leaves, 24, 25
Porphyra, 178
Potash from kelp, 186
Potato, sweet, propagating roots,
67
white, 29, 66, 67, 128
Priestley, on phototropism, 311,
312
Primrose, cultivated, 127
Propagation, artificial, 68-71
vegetative, 63-71, 88, 113, 244,
245
Protective devices of plants, 75
Proteids in seeds, 42, 43
Protoplasm, 11, 12, 27
Pteridophyta, 93, 94
Pulvinus, function, 72-74
Putrefaction, 89, go

[ 387 |

INDEX

Quercus, 116

Radiant energy, and plant life,
287-314
bibilography, 315
Ragweeds, 129, 130
Range, 218-220
Rattan, 113
Ray, 142
Reindeer moss, 93
Reproduction, in plants, 38-71
of brown algae, 177
of diatoms, 182
vegetative, 63-71
Rhizomes, propagation by, 64, 65
Rhodymenia, 185
Ribworts, 128
Rice, antiquity, 209, 210
Indian, 215
wild, 210, 215
Rings of stem, 15
“Ripgut grass,” 232
Root pressure, 5, 6, 23
system, 268, 274
Roots, 4-10
absorption by, 5-9
adaptations for air, 10
functions, 3-5
growth, 5, 6
need of air, 9, 10
phototropism, 312
propagating, 64-66
structure, 4, 5
Rootstocks, propagating, 64
Rose family, 120
Rosette arrangement of leaves, 32
Royal Botanic Gardens, _her-
barium, 150
Rubber, sources of, 121
Rue family, 121
Runners, propagation by, 65-67
Rusby expedition, 355

Russell, Sir E. J., quoted, 298
Rusts of plants, 91
Rye, antiquity, 210

wild, 210

Saccharum, 212
Sage, pollination, 47, 48
Sago palm, 113
Salix, 116
Sand binding by grasses, 226
Sand burs, 230
Sand hills, use of, 227
Sap, defined, 5
flow, 22, 23
of desert plants, 275
osmotic pressure, 275, 278
Saprolegnia, 190
Saprophytes, 31, 288
Sargasso Sea, 88
Sargassum, 88, 89, 171
Saxifrage family, 119
Scales of buds, 20, 21
Scars from leaves, 22
Schedonnardus, 246
Scleropogon, 231
Scrophularia, 128
Scrophulariaceae, 128
Scum, green, 88
Sea, aeration by algae, 188
depth, and plant life, 169, 170
temperature, 168, 169
“Sea lettuce,” 178
“‘Sea-mosses,”” 178
Sea plants, 167-196
and animal life, 187-192
bibliography, 197
Seaweeds, 87-89, 167-197
Sedges, 112
Seed plants, 86-94, 268
Seedling, growth, 63
Seeds, 38, 40, 41-43
dispersal, 55-59
functions, 42

[ 388 ]

INDEX

Seeds, germination, 54, 59-62
viability, 54, 55, 260
winged, 56
Selection in plant development,
342-346
Self-pollination, 43, 44
Sensitive plant, 72-74
Sepals, 41
Sequoias, age, 15
Shirley, quoted, 302
Silage, 224
Sitanion, 232
Slips, 69
Smith, H. M., on Chroococcus, 178
Smithsonian Institution, expedi-
tion to Colombia, 363-371
expedition to Peru, 355
experiments on phototropism,
313, 314
National Herbarium, 150, 152
Smut of corn, as food, 327
Smuts of plants, g1
Soil, origin, 266
Soil water defined, 5
Solomon’s-seal, rootstocks, 64
Sorghum, 342
antiquity, 210, 211
varieties, 211
Sorgo, 211
South America, botanical explora-
tions, 354-356
bibliography, 377
Spanish moss, 114
Spartina, 227-229, 244, 248
Spectrobolometer, 305
Spectrum, electromagnetic, 288
of chlorophyll, 292
of white light, 292
visible, 287, 288
Spencer, H., quoted, 86
Spermatophyta, 94
Sphagnum moss, 93
Spines, origin, 271-273
Spore cases, 40

Spores, 38-40
of algae, 72
of ferns, 267
of seed plants, 268
Sporophyte, 268
Spurge family, 121, 122
Stamens, 41
Starch in plants, 26, 29, 42
Stem, function, 11
growth, 12-17
modifications, 19
structure, 11-14
Stems, 11-22
underground, 64
Stigma of flower, 41, 43
Stipa, 229
Stolons, propagation by, 64
Stomata, 24, 25, 300
Strawberry, pollination, 52
runners, 65, 66
Style of flower, 41
Succulence, 271, 273-279
Suckers, 65, 68
Sugar in plants, 26
Sugar cane, antiquity, 212
cultivation, 212
Sumacs, 122
Sundew, 75, 76
Sunflower seeds, uses of, 130
Sunlight, variation of intensity, 292
Sweet potato called yam, 114
Symbiosis, 92, 93

Tape grass, pollination, 44, 45

Tapioca, 121

Taxonomy, importance, 148, 157-
161

Teff, 211

Tendrils, function, 35-37

Teosinte, 214, 225, 331

Thallophyta, 86-93

Thallus plants, 86-93

Theobroma, 123, 124

[ 389 ]

INDEX

Theophrastus, 134-137
Thorns, origin, 19, 271-273
Time measured by tree rings, 16
Timothy grass, 223, 224
Tobacco, Mammoth, 304
Transpiration current, 23
Tree, adaptations of parts, 3, 4
Tree rings, and climate, 15, 16
chronology, 16
“Tree seaweed,” 176
Trees, adaptations of roots, 10
characteristic scars, 22
deciduous, 21, 22
evergreen, 21, 94, 95
in cities, g, 10
in winter, 17, 19, 20
killed by girdling, 14, 15
orchard, pollination, 52, 53
Tripsaceae, 330, 331
Tripsacum, and maize, 331
species, 332, 334
Triticum, 207
“True grasses,” 203
Trunk, functions, 3, 11
see also Stem
Tubers, of potato, 29
propagation by, 64, 66, 67
Tubes of stem, 15
Tulip-tree, leaves, 118
Tumbleweeds, 56
Twigs, external characters, 17
functions, 3
growth, 16, 17
vascular system, 23, 24
Twining by plants, 34, 36

Ultra-violet rays, 261

Ulva, 178

Umbelliferae, 126

Umbels, 126

Uniola, 236

Upas tree, poison, 75

U.S. Exploring Expedition, 151

U.S. National Herbarium, 150-152
Uses of plants, 97-104

Vanilla, 116
Vascular system, 22-24
Vegetative propagation, 63-71
Venus’s-flytrap, 74
Vine family, 122
Viola, 124
Violet family, 124
Violets, pollination, 124

seed dispersal, 55, 124

Ww
Walnuts, 117
Water lillies, 119
Water plants, 78
Water system, of plants, 311, 312
Water table, 256
Went, on phototropism, 310, 311
Wheat, ancestor, 207
antiquity, 204
cultivation, 323
head, 207, 209
viability, 209
Wild rice, 215
germination, $4
Wilkes expedition, 354
Willow, weeping, 116
Willow family, 116
Wood of stem, 12, 14
Woods from plants, 102, 103, 109
X
Xerophytes, 78, 79, 255, 276
xy
Yam family, 114
Yeast, go
Yucca, pollination, 50, 51
Yucca moth, $0, 51

Zea mays, see Maize
Zizania, 215
Zostera, 168

[ 390 ]

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